7.2.9 Delayed puberty and hypogonadism

Puberty may be defined as the physiological process resulting in the attainment of sexual maturity and reproductive capacity. Puberty is an integral component of the evaluation and treatment of endocrine disorders in children and adolescents. Not only does it impact on sexual maturation, but it has other effects with lifelong consequences, including linear growth, changes in body composition, and skeletal mineralization. Patients with disorders of puberty, including precocious and delayed puberty, make up a large percentage of the children and adolescents who consult paediatric endocrinologists. An understanding of delayed or absent puberty requires a foundation in the normal processes regulating the onset of puberty, and factors essential for its progression and completion. In this chapter, we will first review the mechanisms of normal growth and puberty, particularly with regard to their interdependence. We shall then discuss the differential diagnosis of delayed or absent puberty, and present diagnostic algorithms for hypergonadotropic and hypogonadotropic hypogonadism, emphasizing some gender-specific aspects.

Concurrent with the secretion of sex steroids during puberty, major physical changes, physiological adaptations, and social and emotional challenges occur. The measurement and assessment of these changes are critical for determining whether pubertal development is progressing normally or not, and to monitor the efficacy of treatment.

In boys, the earliest physical change associated with puberty is testicular enlargement, although some boys have pubic hair growth due to adrenal androgens prior to testicular enlargement. Testicular size is commonly assessed by using a series of calibrated, testis-shaped ellipsoids (beads) called the Prader orchidometer. If this is not available, the long axis of the testis can be measured using simple calipers or an ordinary tape measure. Prepubertal testes are smaller than 4 ml in volume and less than 2.5 cm in length. As puberty ensues, the testes gradually enlarge, mainly due to increases in volume of the seminiferous tubule content, and eventually reach the adult volume of 15–25 ml or length of 4–5 cm. Physical changes accompanying testicular enlargement include thinning of the scrotal skin, apocrine sweating and adult body odour, and the growth of sexual hair. Additional changes present in boys include an increase in muscular size and strength, and body hair growth in a typical adult male pattern. Deepening of the voice occurs during the second half of pubertal development.

Genital development in boys is often assessed using the method of Tanner. Two rating scales are used in males: one for pubic hair growth, and another for enlargement of the testes, penis, and scrotum. Tanner stages for boys are reviewed in Table 7.2.9.1. Briefly, pubic hair growth starts as fine, straight, lightly pigmented hairs, generally located on the pubic symphysis at the base of the penis. As puberty progresses, the hair becomes coarser and curly, with darker pigmentation. At Tanner stage 5, the growth extends down the medial thighs and up the lower abdomen. Genital Tanner stages are somewhat more subjective. The early stage of puberty consists of testicular enlargement only, followed by gradual enlargement of the penis, first in length and then in circumference, and enlargement of the testes to reach full adult development (1).

In girls, the first clinically apparent sign of puberty is breast development, although pubic hair growth precedes breast development by up to 6 months in approximately 30%. It is common for one breast to grow for several months before the other, and mild asymmetry is often present. Pubic hair growth usually begins within 6 months of the onset of breast development. As oestrogen levels increase, changes occur in the vaginal mucosa. In the prepubertal girl, the vaginal epithelium is thin with a dark red colour, and consists mainly of basal and parabasal cells. With advancing pubertal development, the epithelium proliferates and thickens. Intermediate and superficial cornified squamous cells overlay the parabasal cells, and give the mucosa a pink, opalescent appearance. This is often accompanied by a physiologic vaginal discharge.

The progression of puberty in girls is also assessed with Tanner staging. Pubic hair in girls is assessed using the same hallmarks as in boys, although normal girls with Tanner stage 5 pubic hair do not have extension up the lower abdomen (Table 7.2.9.1). Some physicians add a Tanner stage 6 in girls to describe those with pubic hair extension both to the medial thighs and in the midline of the lower abdomen. Breast development is commonly measured using Tanner staging as well and this is depicted in Table 7.2.9.1. Breast development begins at Tanner stage 2 with budding, in which there is a firm palpable disc of tissue not larger than the areola. In stage 3, the diameter of the tissue exceeds the areola but does not have stage 4 morphology. Stage 3 encompasses a large range of development, from very early in puberty up to the later stages of development. With stage 4, there is a ‘double contour’ in which the profile of the areola is distinct from the profile of the breast. Although stage 5 is considered to be full adult development, some normal adult women do not progress beyond stage 4, and some never develop a double contour, skipping stage 4 altogether (2).

The clinical hallmark of puberty as it relates to body size is the pubertal growth spurt. In boys, the peak of the growth spurt is timed to Tanner stage III-IV, whereas in girls the peak occurs earlier in puberty, typically at Tanner stages II–III. The average peak growth velocity in boys is 9.5 cm/year, and in girls it is somewhat less, 8.3 cm/year. The later onset of puberty, the later occurrence of the growth spurt within puberty in boys, and the greater magnitude of the growth spurt combine to result in an average height difference between the sexes of 13 cm.

Puberty also has effects on skeletal maturation, and the timing of puberty is more closely correlated with the bone age than with chronological age. In European girls, the average bone age at the time of thelarche is 10.5 years (95% confidence limits 8.5–13.2), and at the time of menarche it is 12.8 years (11.3–13.6). In girls, the peak height velocity occurs at a bone age of 12 years. In boys, the average bone age at stage 2 of puberty is 11.5 years (9.0–14.2). At peak height velocity in boys, the bone age ranged between 11.9 and 15.5 years in one study, and between 12.5 and 16 years in another study (3, 4).

Children with advanced bone ages typically enter puberty earlier than their peers, while those with delayed bone ages enter puberty later. Factors that alter the bone age also alter the timing of puberty, and these may include sex steroids and the growth hormone/insulin-like growth factor 1 (IGF-1) system (4).

There is a great deal of disagreement about the age at which pubertal development is normal. Most of this disagreement relates to the lower age limit of normal. There is evidence that the age of onset of puberty has decreased in the last several decades in both girls and boys. For boys, data show that the average age at Tanner stage 2 development is between 11.2 and 12.4 years. The normal range of attainment of stage 2 puberty in boys is commonly considered to extend from 9 to 13.5 years. For girls, there is more disagreement. Historically, the normal range of onset of puberty has been between 8 and 13 years, but the lower limit of normal may extend down to 7 years for white girls and 6 years for black girls. A recent analysis of data from the Third National Health and Nutrition Examination Survey (NHANES) in the USA revealed that body mass index (BMI) is an independent predictor of the age of onset of puberty, with earlier occurrence of breast and pubic hair development and earlier menarche in girls with BMI above the 85th percentile (5). The upper limit of 13 years for girls remains generally accepted. The tempo of pubertal development is also important to consider. Girls starting puberty earlier than average tend to have a slower progression to menarche than girls starting puberty later. Hence, the age at menarche has less variability than the age at thelarche and is about 12.6 years. This phenomenon also probably occurs in males, but the lack of a clearly definable events such as menarche in male puberty makes study difficult (6–9).

The hypothalamic-pituitary-gonadal axis is active in utero, with peak secretion of gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) occurring between 20 and 24 weeks gestation. During later pregnancy, levels drop as the negative feedback effects of gonadal hormones intensify. In both males and females, there is a ‘minipuberty of infancy’ that occurs during the first few months after birth. Beginning at birth, gonadotropin levels begin to increase under the influence of GnRH, possibly stimulated by withdrawal of placental oestrogens. In girls, the increase in FSH is particularly robust. Sex steroid levels also increase and the serum testosterone in boys often reaches 5.2 nmol/L or greater during the mini-puberty of infancy (10). Testosterone peaks at 2–3 months of age in males, while oestradiol peaks at about 4 months in females. By 5–6 months of age, the negative feedback effects of sex steroids are beginning to be re-established, and GnRH secretion, LH and FSH levels, and gonadal steroid levels fall to their prepubertal levels. This cessation of activity is known as the juvenile pause. It may be related to increases in hypothalamic oestrogen receptors, allowing negative feedback to intensify. The suppression of HPG activity may be incomplete in some females and this may result in transient oestrogen secretion, giving rise to the clinical picture of premature thelarche. Over the course of the next several years, the juvenile pause persists, reaching the greatest degree of axis suppression in females at about age 6 years.

GnRH is released from the hypothalamus in a pulsatile fashion, with the pulses in prepubertal children being small in amplitude and somewhat irregular. The frequency of the pulses is roughly once every 1–2 h. In females, as the age of clinical puberty approaches, the amplitude of the pulses begins to increase (Fig. 7.2.9.1). The average age for this to occur is 7–10 years of age. Hence, before clinical signs of puberty are noted, early endocrine changes have begun. Initially, this increase in GnRH pulse amplitude occurs during the night, and daytime pulse amplitude remains low. The pulsatile GnRH secretion is reflected in gonadotropin secretion. The pulses in LH secretion can be detected by careful serial measurement of LH concentrations using sensitive assays. Although FSH is also released in a pulsatile manner in response to pulsatile GnRH, variations in the serum FSH are not apparent, perhaps due to the longer circulating half-life of FSH. FSH levels in females are typically higher than LH levels, and this may play a role in stimulation of ovarian follicular growth and development. Higher overnight gonadotropin concentrations result in higher testosterone levels in boys and an increase in oestradiol levels in girls. In early pubertal boys, testosterone levels are highest overnight and in the early morning hours. In early pubertal girls, oestradiol levels peak in the mid-morning, about 12 h after the peak of LH secretion.

Using current standard immunoassays for testosterone and oestradiol, which lack sensitivity at low concentrations, the morning increases in sex steroid levels may be difficult to detect during the very earliest stages of puberty. However, more modern techniques, especially liquid chromatography/tandem mass spectrometry (MS) can usually detect even the lower prepubertal levels. In early puberty, gonadotropin levels also may be difficult to distinguish from normal prepubertal levels, in part due to the pulsatile nature of their secretion and in part due to the low amplitude of secretion during the daytime. These factors make the routine laboratory evaluation of delayed puberty difficult, because casual gonadotropin and sex steroid levels do not differentiate a patient who is nearing a normal, but delayed puberty from one who will never enter puberty due to a pathological condition. However, as GnRH pulsatility increases in early puberty, pituitary stores of LH also increase. These stores may be released following acute stimulation by GnRH. This is the basis for the GnRH stimulation test, which may be positive even before physical changes of puberty become clinically apparent.

With progressing pubertal development, there is a further expansion of pulsatile GnRH secretion, with the amplitude and the frequency of the pulses increasing (Fig. 7.2.9.1). Instead of being confined to the night, larger amplitude pulses are now also produced during the daytime. The pulse frequency becomes more tightly regulated, occurring virtually hourly. Gonadotropins continue to be released in a pulsatile fashion, but the baseline levels are also increased above prepubertal concentrations. Additionally, there is a shift in the glycosylation pattern of LH towards forms that are more biologically active. As GnRH, LH, and FSH secretion increase, so does sex steroid secretion, and the marked diurnal variation in testosterone and oestradiol levels is damped. In girls, LH levels increase 25–40-fold relative to levels present before puberty. Oestradiol concentrations increase from less than 8 pmol/L before puberty up to more than 368 pmol/L in a postmenarchal girl. Testosterone concentrations in prepubertal males generally are below 0.35 nmol/L, and in young adults they are above 10.4 nmol/L.

The timing of puberty is a complex trait and in the general population it has a Gaussian distribution. There are many influences on the regulation of pubertal timing, including nutritional factors, environmental influences, and genetic input. Complex traits often demonstrate a high degree of genetic regulation, and it is estimated that between 50 and 80% of the variance of normal pubertal timing is explained by genetic factors. Efforts to understand the genetics of pubertal timing have led to the discovery of many genes that are clearly necessary for pubertal development. Many of these genes, when mutated, lead to specific syndromes of delayed or absent puberty, which are discussed below. These include defects in GnRHR, KAL1, FGFR1, TAC3. TACR3, LEP, LEPR, KISS1, GPR54, PROK2, and PROK2R. However, it is not clear that these genes individually or as a group explain much of the variability of the onset of normal puberty. The onset of puberty is almost certainly controlled by a polygenic mechanism. Genome-wide association studies and other high throughput technologies have shown promise in elucidating regulatory systems for complex traits. Such studies are likely to reveal a large number of involved genes, each playing only a small role, but collectively explaining much of the variance. These techniques, however, may be limited by statistical issues that affect their reproducibility.

In 2003, the kisspeptin/GPR54 system was discovered to be a key regulatory factor in the initiation of increased GnRH pulsatility at the onset of puberty (11). Kisspeptin is produced by hypothalamic neurons in the arcuate and periventricular nuclei, and interacts with its receptor, GPR54, on GnRH secreting neurons. Kisspeptin expression increases with the physiological onset of puberty in several mammalian species. In humans, inactivating mutations of this system have been associated with delays in puberty, while an activating mutation has led to precocious puberty (12). In multiple animal systems, including humans, exogenous administration of kisspeptin increases the pulse amplitude of GnRH. Administration of kisspeptin to healthy male volunteers causes increases in LH and testosterone concentrations. The kisspeptin/GPR54 system may also be involved in negative and positive feedback effects of sex steroids on GnRH secretion. Although it is clear that kisspeptin plays a role upstream of GnRH, the factors regulating its release are not presently known (13).

Both inhibitory and stimulatory factors in the central nervous system are involved in the initiation of puberty. γ-aminobutyric acid (GABA)-secreting neurons play an inhibitory role and may be involved in the juvenile pause, the temporary suppression of the hypothalamic–pituitary–gonadal axis that occurs during childhood. Suppression of GABAergic neuronal input may lead to the initiation of puberty. Additional factors may include increased glutamate stimulation of N-methyl-d-aspartate (NMDA) receptors, which are stimulatory to GnRH release. Leptin, acting through its receptor, links nutritional status to puberty, and sufficient levels of leptin are thought to be required for the initiation of puberty. Melatonin secretion from the pineal gland suppresses puberty in lower mammals, but has no clear effect in humans.

During puberty, growth hormone secretion is augmented, largely due to increases in pulse amplitude. This increase is mediated by increases in circulating oestrogens and androgens. The higher growth hormone secretion in turn leads to increases in IGF-1 production by the liver, resulting in circulating IGF-1 concentrations in adolescents that are 2–3 times those in adults. Additionally, aromatizable androgens potentiate the effect of growth hormone on IGF-1 production, resulting in further increases. The higher growth hormone concentrations also lead to increases in local production of IGF-1 in cartilage. Increases in IGF-1 not only lead to more rapid growth, but also potentiate the effects of puberty by increasing ovarian FSH receptors. Higher growth hormone levels increase granulosa cell steroidogenesis.

The causes of delayed puberty and hypogonadism can be divided into those involving delays or defects in hypothalamic regulation of the initiation of puberty and those involving primary defects of the gonads. These groups of conditions are best differentiated by the serum concentrations of gonadotropins after the age when puberty is expected. Hypothalamic and pituitary deficiencies are termed hypogonadotropic hypogonadism or central hypogonadism, and primary gonadal disorders are termed hypergonadotropic hypogonadism or primary hypogonadism.

Constitutional delay of growth and puberty (CDGP) is a common variant of physiological (normal) maturation. Its major outward characteristics include a slowing of the growth rate, as well as a delay in the timing (and perhaps tempo) of puberty. The typical patient is a boy (or his parents) who seeks endocrinological evaluation in the early teenage years because the discrepancy in growth and adolescent development between the patient and his/her age peers causes significant concern (Fig. 7.2.9.2).

Clinically, the height age (the age for which the patient’s height is on the 50th centile) is delayed with respect to the calendar age, but is concordant with the ‘biological age’ as indexed by the bone age. Sexual development is either prepubertal or lagging behind that of their peers, although it is often appropriate for the bone age. The height velocity is normal for a prepubertal child, although it may decline to subnormal values if the delay is more than 2–3 years (pre-pubertal ‘dip’). When the height is plotted on the standard growth curve, the height gain appears to be ‘falling off’ the previously defined height centile, since the standard growth curve incorporates the pubertal growth spurt at an ‘average’ age. This discrepancy in growth between the normal adolescent and the one with CDGP only accentuates the difference between age-matched peers. This discrepancy, as well as the delay in pubertal maturation, is often a compelling concern of the patient or the family, and brings the adolescent to medical consultation. Tanner has devised longitudinal growth curves that account for the later growth and adolescent development, because this pattern is so common.

Biochemically, adolescents with CDGP resemble their peers with comparable biological (bone) ages. Thus, the pubertal increases in haemoglobin, haematocrit, creatinine, and alkaline phosphatase will not be present. Serum levels of growth hormone (pulsatile pattern), IGF-1, IGFBP-3, LH, FSH, and the sex steroids may be diminished for chronological age, but normal when compared with younger adolescents of the same stage of sexual development. The suppressed HPG axis found in adolescents with CDGP represents an extension of the physiological hypogonadotropic hypogonadism (the ‘juvenile pause’) noted since infancy.

Without intervention with sex steroids, most adolescents with CDGP will undergo spontaneous pubertal development and will reach their target height range as calculated from parental stature. Development occurs as much as several years after that of their peers. Many adolescents find that intolerable and suffer significant emotional distress because they differ in their appearance from their peers during these years. That is often the rationale for the short-term use of gonadal steroid therapy. Linear growth and a more mature ‘appearance’ are more objective outcomes of gonadal steroid administration.

There are many causes of combined pituitary hormone deficiency, both congenital and acquired, which may include deficiency of GnRH or gonadotropins. These conditions are reviewed elsewhere in this text.

The neuroendocrine control in mammalian reproduction is governed by a single gene coding for GnRH. A neural network of approximately 1500–2000 neurons integrates various upstream genes that are responsive to environmental cues, such as food (energy) availability, stress, and perhaps light–dark cycles (at least in seasonally breeding mammals).

A cascade of signalling molecules and transcription factors plays a crucial role in pituitary development, cell proliferation, patterning, and terminal differentiation (14). Genes are expressed in an orderly sequence to activate or inhibit downstream processes (target genes) that have specific roles in the terminal differentiation of pluripotent precursor cells. Mutations involved specifically in human hypothalamic-pituitary disease are listed in Table 7.2.9.2. It should be noted, however, that there is increasing evidence that disorders of puberty may result from multiple genetic mutations, with some disorders presenting from the cumulative burden of mutations in genes such as FGFR1 and GnRHR (see below). These broaden the phenotypic spectrum and the endocrine profiles of the subjects.

KS is the combination of hypogonadotropic hypogonadism (HH) and a diminished sense of smell—hyposmia or anosmia. It is mainly due to a failure of the GnRH neurons, which have an extra-central nervous system (CNS) origin in the nasal placode, to leave their origin and follow the olfactory epithelium to migrate into the CNS. This is accomplished via the olfactory bulb and tract, finally ending at the arcuate nucleus of the hypothalamus. These neurons form a network among themselves and project dendrites towards the median eminence. With an as yet undiscovered mechanism, the neural network forms pulses of GnRH, which travel to the median eminence, are secreted into the hypothalamic-pituitary portal system, and then cause the pituitary gonadotropes to produce LH and FSH pulses in the general circulation. These activate the gonads to produce testosterone or oestrogen/progesterone.

(OMIM 308700) The first gene discovered to cause KS was KAL1, whose protein product, anosmin, has neural cell adhesion properties and is apparently secreted from the olfactory neurons (15, 16). It is an absolute requirement as a scaffold for the GnRH neurons to traverse the cribriform plate and take residence in the arcuate nucleus. In addition, subjects with KAL1 deficiency lack olfactory epithelium, the olfactory bulb and tracts. Associated anomalies include synkinesia (mirror movements of the extremities), unilateral renal agenesis, oculomotor abnormalities, sensorineural hearing loss, and midline facial clefts. The mode of inheritance is X-linked recessive, and it is approximately 10-fold more common in males. This gene generally separates those with KS from those with normosmic idiopathic hypogonadotropic hypogonadism (nIHH), which presents similarly to KS, but with an intact sense of smell. However, individuals with classic KS and nIHH may be seen in the same kindreds. The phenotype has been identified a number of times—IHH subjects present with a lack of sexual maturation at the appropriate age associated with inappropriately low gonadotropin levels in the presence of prepubertal concentrations of sex steroid hormones, normal anterior pituitary function, and normal findings on brain imaging and response to exogenous pulsatile GnRH administration.

A few years after the discovery of the KAL1 gene came the isolation of an entirely new gene called GPR54 and its cognate ligand, a 54 amino acid peptide comprising residues 68–121(also known as metastin) of the 145 amino acid residue precursor, Kisspeptin-1 (11, 15). This ligand-receptor complex acts upstream from GnRH. GPR54 is a G-protein-coupled receptor gene that, when mutated, causes autosomal recessive nIHH in both mice and humans, suggesting that it is an obligatory upstream controlling mechanism for pulsatile GnRH secretion. Subjects with mutations in the GPR54 gene present similarly to those with KS. They lack pubertal development at the appropriate time, but have an intact sense of smell. Male and female subjects with mutations in the GPR54 peptide achieve fertility and normal pregnancy following either exogenous gonadotropin therapy or long-term, pulsatile GnRH administration. As more mutations have been found, the phenotype has expanded to delayed puberty, rather than absent pubertal development. These findings solidify the position of the kisspeptin/GPR54 system acting before (upstream of) GnRHR. Proposed mechanisms for the action of the GPR54/Kisspeptin pathway include the following.

FGFR1 is one of four tyrosine kinase receptors for the much larger family of FGF ligands (at least 23 members). Patients with mutations in FGFR1 may have KS with anosmia or they may have nIHH. The inheritance is autosomal dominant. This suggests not only that FGFR1 (and perhaps one of its yet undiscovered ligands) may be required for the migration of GnRH neurons across the olfactory apparatus, but also strongly suggests that an entirely different mechanism exists for the failure of pulsatile GnRH secretion in the subjects with an anatomically normal olfactory system. A further novel finding was that some who clearly met the criteria for nIHH subsequently had normal puberty, sexual maturation and fertility after receiving sex-hormone replacement therapy. Ten percent (5/50) of the subjects in one large series showed this phenotypic response, including increased testicular size (evidence for sustained gonadotropin secretion), pulsatile LH secretion, adult levels of testosterone, and a normal ejaculate and sperm count (15, 17). Isolated anosmia has also been identified within families with FGFR1 mutations.

Several patients with homozygous frame shift mutations in the GNRH1 gene have been reported(18, 19). Affected males had cryptorchidism and microphallus, and both males and females exhibited a complete absence of pubertal development, low gonadotropin concentrations, and low serum levels of testosterone and estradiol, respectively. The patients were normosmic, and there were no other associated abnormalities. In addition, Chan, et al identified several heterozygous variants in patients with nIHH which are of uncertain significance(19).

GnRHR is a G-protein coupled receptor expressed on the gonadotropes. Mutations result in impaired GnRH binding, intracellular trafficking, recycling, or signal transduction and cause a spectrum of defects from completely deficient to partial insufficiency of the HPG axis. The mode of inheritance is autosomal recessive. Reports of several series of subjects with nIHH have noted a frequency of GnRHR gene mutations ranging from 3.5 to 10.4% (18).

The prokineticin system is composed of two very similar receptors (GPR73, a and b) within the rhodopsin receptor family, analogous to GPR54. These receptors have two polypeptide ligands, PROK1 and PROK2. The former and its receptor, PROKR1, are primarily found in the gastrointestinal tract, but PROK2 and PROKR2 are located in the neuroendocrine areas, including the arcuate nucleus, olfactory tract, and the suprachiasmatic (clock) nucleus. The phenotype includes abnormal development of the olfactory bulbs combined with hypogonadotropic hypogonadism. Humans with mutations in PROK2 or PROKR2 may have the Kallmann or the nIHH phenotype and endocrine profile (15).

It has been estimated that mutations in the TAC3/TACR3 system may be responsible for over 5% of cases of nIHH (21). These genes code for neurokinin B and its receptor, respectively. Neurokinin B is co-located in neurons expressing kisspeptin, although its functional role in these cells is unknown. Neurokinin B and its receptor are also expressed in other reproductive tissues, including the uterus and ovary. The majority of the patients identified as having mutations in this system have had abnormalities in TACR3 (21, 22). Nearly all of the male patients had micropenis, but testicular volumes varied, suggesting some degree of testicular function. Interestingly, many affected individuals appear to have had partial or complete recovery of gonadal function in adulthood when observed off of treatment (21). A smaller number of patients with mutations in the TAC3 gene have been described. However, the phenotype of these individuals is indistinguishable from those with mutations in the receptor, including the potential for gonadal recovery.

Deficiency of leptin leads to a phenotype of early and severe hyperphagia, accelerating weight gain, insulin resistance, impaired T-cell function and nIHH as an adolescent (19). The circulating leptin concentrations are below the level of sensitivity of the common leptin assays. Although thyroid, adrenal and somatotropic functions are normal, the levels of gonadotropins and sex-steroids are within the prepubertal range as is the physical examination. Pulsatile LH secretion is absent; however, with administration of recombinant human leptin, marked changes in body composition (decreased fat mass) and adolescent development occurred (20). Those with mutations of the leptin receptor have the same phenotype except that the leptin levels are elevated, and the response to exogenous leptin is absent or attenuated. Recombinant human leptin administration prevented the experimental disruption of LH pulsatility induced by fasting and restored menstrual cyclicity in some women with functional hypothalamic amenorrhea (21).

DAX1 is an orphan nuclear receptor predicted to be a transcription factor important in the development of the adrenal cortex and gonadotropes. Loss of function of DAX1 (Xp21) leads to an X-linked recessive disorder characterized by hypogonadotropic hypogonadism and adrenal failure without the hyperandrogenism of virilizing congenital adrenal hyperplasia. Patients with this disorder, called adrenal hypoplasia congenita, have both glucocorticoid and mineralocorticoid deficiencies, and hypogonadotropic hypogonadism, which may not be manifest until the second decade of life. The mode of inheritance is X-linked recessive. DAX1 is a negative regulator of SF1-mediated activity. A double dose is associated either with a female phenotype or ambiguous genitalia in XY males. Puberty is usually delayed, especially in boys, and a diagnosis of nIHH can be made at the appropriate age. Some may have a mixed picture of partial nIHH with an added defect at the gonad, illustrating the importance of DAX1 and SF1 for steroidogenesis (22).

This is another of the monogenic obesity syndromes that may include nIHH. Few subjects have been described, at least one of whom died in infancy without being able to define a pubertal phenotype (18).

Inactivating mutations of the human LHβ subunit lead to nIHH in men and women (23). All male subjects had normal genitalia at birth, no pubertal development and infertility. The mode of inheritance is autosomal recessive. Circulating LH levels are undetectable, without an LH response to exogenous GnRH administration.

One female subject with two brothers having nIHH due to LHβ deficiency presented with full sexual development and secondary amenorrhea and infertility. Menarche occurred at 13 years. She had premature menopause, but remained hypogonadotropic (23). Thus, there can be widely disparate phenotypes with the same mutation, especially as modified by gender. A specific explanation is lacking for the normal spontaneous pubertal development and subsequent premature menopause in the affected woman described above.

Females with isolated deficiency of the FSHβ subunit present with delayed pubertal development and primary amenorrhoea, normal or high levels of LH, and low or undetectable levels of FSH. Males have normal pubertal development, but small testes and oligospermia. Exogenous GnRH administration raises LH, but not FSH levels (24).

Mutations in this gene are found in the majority of patients with CHARGE syndrome (Coloboma of the eye, Heart defects, Atresia choanae, Retarded growth and development, Genitourinary defects, and Ear abnormalities). Some affected patients have pituitary defects, including growth hormone deficiency and HH. Some patients initially identified as having Kallmann syndrome have been subsequently reclassified as having CHARGE syndrome based on the presence of ear abnormalities and detection of mutations in CHD7 (29).

The prevailing concept in this arena is that of energy conservation or the laws of thermodynamics. One must have ‘enough’ energy to support body growth and to store energy, predominantly fat, for longer-term energy requirements, such as the menstrual cycle, pregnancy, and lactation (25). The concept is that for current energy requirements

Energy retention = [energy intake (EI) – energy expenditure (EE)]

In experiments with female athletes, Loucks modified this to:

Energy availability (EA) = [EI – exercise EE]/fat-free mass (FFM)

The latter equation takes into account that it is the FFM that is the metabolically active (fuel burning) tissue and emphasizes how EA may be reduced by either restricting EI or increasing exercise EE (EEE) (25).

This latter equation may be rearranged to make the message clearer for experimental studies:

EI = EEE + [EA × FFM]

Randomized clinical trials controlling both EI and EEE have shown that energy balance occurs at EA = 45 kcal/kg FFM per day in healthy young women, and that there is damped pulsatile release of LH after 5 days of EA below 30 kcal/kg per day, which roughly corresponds to the resting metabolic rate in healthy young adults. The susceptibility of the HPG axis to alterations in EA is strongly age dependent as might be hypothesized from the very high incidence of subclinical menstrual disorders shortly after menarche. This concept was experimentally tested by decreasing the energy availability to 25 kcal/kg FFM per day in gynaecologically younger (5–8 years after menarche) and older (14–18 years after menarche) young women. After 5 days of caloric restriction and exercise, it was noted that only the gynaecologically younger women had disrupted pulsatile release of LH. Thus, the gynaecologically older women had a more ‘robust’ HPG axis, and the data likely explain the high incidence of ‘athletic amenorrhea’ in young women with the female athlete triad: eating disorder, osteopenia and amenorrhoea (25).

Treatment may be difficult. The most straight forward approach would be to prescribe a greater caloric intake or to decrease exercise energy expenditure. This is a difficult treatment plan for a highly competitive athlete, probably a gymnast, dancer, or long-distance runner. The American Academy of Pediatrics Committee of Sports Medicine and Fitness, 1999–2000 has presented a series of recommendations. Those relevant to the female athlete triad are shown in Box 7.2.9.1.

The karyotypic abnormality consisting of two or more X chromosomes and one or more Y chromosomes is known as Klinefelter syndrome. Klinefelter syndrome is the most common defect of chromosome number, with a prevalence of 1:500–1:1000 in the general population. It is thought that many males are undiagnosed, even in adulthood. Infants and young children often have problems with expressive language development, and school-aged children may have difficulty with reading and behaviour. Psychological testing often shows disorders of executive function as well. Physically, the testes appear normal during infancy and childhood, and levels of FSH and LH are normal before puberty. As pubertal development unfolds, the testes do not increase in size normally, and the seminiferous tubules gradually become hyalinized, with loss of germ cells and Sertoli cells. Clinically, the testes remain small and may become very firm to palpation. In one study, the mean testicular volume was 5.5 ml (26). LH and FSH levels begin to rise into the upper portion of the normal adult range early in puberty. By mid-puberty, LH and FSH concentrations are often abnormal. Although the onset of puberty is typically normally timed, 80% of affected individuals do not achieve normal adult concentrations of testosterone. The abnormal testosterone secretion results in a slow tempo of physical changes and lack of attainment of normal pubic hair, and other sexual hair growth, as well as small penis size and lack of muscular development. The relatively low levels of testosterone and high concentrations of oestradiol predispose adolescents and adults to gynaecomastia, which occurs in about 40% of affected individuals.

Essentially all affected men with Klinefelter syndrome have azoospermia or severe oligospermia and are infertile. However, intracytoplasmic germ cell injection (ICSI) has proven to be a feasible approach for those who have viable spermatozoa isolated from ejaculates or after testicular sperm extraction (TESE).

Partial or complete loss of one of the two X chromosomes in females is known as Turner syndrome. Turner syndrome has an incidence of 1:2000 live born female infants. Turner syndrome is the most common cause of first trimester spontaneous abortions, and only about 1% of 45,X conceptuses are liveborn. The most common karyotype is 45,X, comprising about 50% of affected girls. Most of the remainder have various forms of mosaicism or partial deletion, usually including loss of at least the short arm of the second X chromosome.

The ovaries of affected fetuses show accelerated loss of germ cells. At birth, the oocyte number is reduced to far below normal. The high rate of oocyte loss continues, and the ovaries of affected girls are typically depleted of germ cells within a few years of birth. Classically, girls with Turner syndrome fail to enter puberty, with an absence of breast development. Pubic and axillary hair typically develop normally due to adrenal androgen production. However, approximately 20% of girls will have spontaneous breast development, more commonly those with mosaic or partial forms of Turner syndrome. Spontaneous menses can occur, again most often in girls with mosaic forms, although secondary amenorrhea nearly always develops. Pregnancy may very rarely occur (27).

Gonadotropin levels in the neonatal period and infancy may be normal. In early and mid-childhood, LH and FSH concentrations are also normal, due to the high degree of negative feedback of low levels of oestrogen on the hypothalamus and pituitary. However, by late childhood and early adolescence, gonadotropin levels are often elevated well above the adult range. A karyotype is necessary to confirm the diagnosis and should be obtained regardless of the presence of physical stigmata of Turner syndrome.

The 47,XXX karyotype is common, with a prevalence of 1:900–1000 in the general population. There are few or no recognizable phenotypic features of the condition, although reports indicate that affected individuals are taller than average. There is a higher than normal incidence of neurodevelopmental disorders, such as poor attention span, academic difficulties, decreased verbal fluency, and poor spatial cognition. Although ovarian function is usually normal, primary ovarian dysfunction occurs in a subset of individuals. This may present as delayed puberty or as premature ovarian failure. In studies of adult women with premature ovarian failure, the 47,XXX syndrome occurs in about 1–2% of patients. Gonadotropin levels are elevated, and a karyotype analysis is diagnostic (28). Females with larger numbers of additional X chromosomes (48,XXXX or 49,XXXXX) are more likely to have phenotypic and developmental abnormalities.

A large number of genes important for normal ovarian function reside on the long arm of the X chromosome. Deletions of portions of Xq and balanced translocations with breakpoints on Xq are associated with ovarian dysfunction. The location of breakpoints associated with hypergonadotropic hypogonadism cluster in two regions, Xq13.3–21.1 and Xq26-qter. The ovarian dysfunction may take the form of either primary or secondary amenorrhea (29).

XY and XX gonadal dysgenesis are terms describing heterogeneous groups of disorders of gonadal differentiation. Affected individuals typically have normal female genitalia and are often not recognized until they fail to enter puberty. Those with XY complete gonadal dysgenesis (Swyer syndrome) have failure of testis determination early in fetal life, with formation of a streak gonad and subsequent failure to secrete testosterone, and müllerian inhibiting substance (MIS). In the absence of testosterone and MIS, both internal and external genitalia develop along female lines. If partial testis determination occurs, leading to partial Leydig and Sertoli cell function, incomplete masculinization of the internal and external structures occur, resulting in ambiguous genitalia. Abnormalities of several genes have been implicated as causes of XY complete gonadal dysgenesis, including defects in SRY, accounting for 10–15% of children (30); defects in WT1, associated with Denys–Drash and Frasier syndromes; abnormalities of SOX9, associated with camptomelic dysplasia; SF1, associated with adrenal hypoplasia; and duplication of DAX1. In addition to absent puberty, affected individuals have a 30% incidence of gonadal tumours, most commonly gonadoblastoma and dysgerminoma (31). Spontaneous pubertal changes in a patient known to have XY complete gonadal dysgenesis should prompt a search for a sex steroid-secreting gonadoblastoma.

Girls with XX gonadal dysgenesis do not have stigmata of Turner's syndrome, but they are typically somewhat shorter than average. Similar to individuals with Swyer's syndrome, they have normal female internal and external genitalia. Ovarian histology ranges from fibrous streaks to hypoplastic ovaries. Gonadal tumours are uncommon in this population. One identified cause of 46,XX gonadal dysgenesis is FSH resistance caused by a mutation in the FSH receptor (see below).

Those affected by either XY or XX gonadal dysgenesis have elevations of gonadotropin levels by the time of expected puberty. Karyotype analysis will reveal the diagnosis in 46, XY patients, and imaging studies of the pelvis will show absent ovaries. 46, XX gonadal dysgenesis must be distinguished from premature ovarian failure caused by a number of other conditions, including autoimmune oophoritis or exposure to radiation or chemotherapeutic agents.

Complete androgen insensitivity syndrome (CAIS) is caused by mutations in the androgen receptor gene. The prevalence of CAIS has been reported to be between 1: 20 400 and 1: 99 000 genetic males (32).

At the time of puberty, testicular secretion of testosterone occurs, and testosterone levels typically rise into the adult male range or higher. Because of the androgen resistance, there are few or no clinical signs of androgen action, such as pubic or axillary hair. Breast development appears to proceed normally, caused by aromatization of circulating testosterone. Primary amenorrhoea occurs because of the absence of the uterus.

Gonadotropin levels are often normal at birth and typically are in the normal prepubertal range during childhood. As the age of normal puberty ensues, LH secretion increases because of the lack of negative feedback from testosterone via the androgen receptor. High testosterone and LH concentrations in a female with clinical signs of androgen resistance and with a history of amenorrhea are virtually diagnostic, and the diagnosis is then confirmed with a karyotype demonstrating a 46,XY composition. Genetic testing is available, but there are several hundred described mutations.

Galactosaemia is an inborn error of metabolism most commonly caused by a mutation in the gene for galactose-1-phosphate uridyltransferase. Premature ovarian failure occurs in 75–96% of female patients with galactosaemia. The age at onset of ovarian dysfunction ranges from childhood to adulthood, and patients may present with absent puberty, or may have normal pubertal development and menarche, but develop secondary amenorrhea later. Ovarian function may wax and wane, with periods of amenorrhea alternating with spontaneous ovarian cycles and possible fertility. Those individuals harbouring more severe mutations are more likely to experience consistent and lifelong ovarian failure. The effect of heterozygosity for galactosaemia on ovarian function remains controversial (33).

The mechanism of ovarian damage in cases of galactosaemia is unknown. Ovarian tissue has a high content of galactose and its metabolites, and normally has high galactose-1-phosphate uridyltransferase activity. In contrast, the testis has low enzymatic activity and low galactose content, presumably accounting for the absence of testicular dysfunction in males with galactosaemia. It is thought that accumulation of galactose and galactose-1-phosphate in ovarian cells has direct cytotoxic effects by decreasing the activity of a number of metabolic pathways.

Defects in the receptors for LH and FSH are very rare causes of abnormal pubertal development. The LH receptor in the male is critical for normal testosterone secretion in utero. Hence, partial loss of LH receptor function (OMIM 152790) causes inadequate testicular secretion of testosterone and ambiguous genitalia in the 46, XY fetus. Alternatively, complete loss of the LH receptor leads to an inability to secrete any testosterone and a subsequent lack of masculinization of the 46, XY fetus and normal female external genitalia. If the individual is assigned to the female sex and not diagnosed early in life, there is complete absence of pubertal development and primary amenorrhea, as the testicular tissue will not secrete testosterone and there will be no aromatization to oestrogens. Females with loss of LH receptor function usually have normally timed breast development but experience primary or secondary amenorrhea and hypoestrogenemia. This highlights the importance of normal FSH activity for females in early puberty and the importance of LH activity to establish normal menses and oestrogen levels in later puberty and adulthood (34).

Abnormalities of the FSH receptor (OMIM 136435) have mainly been described in the Finnish population. Females carrying mutations in the FSH receptor gene usually present with 46,XX gonadal dysgenesis, with absent puberty and primary amenorrhea. Some affected individuals, however, will have spontaneous pubertal development and even menarche, although those identified as having the disorder have all become amenorrhoeic. Males with defects of the FSH receptor have normal pubertal development, normal testosterone levels, and normal or near normal gonadotropin levels. However, they may have oligospermia (35).

In addition to those discussed above, a large number of other single gene defects and genetic syndromes are associated with hypergonadotropic hypogonadism. Defects of steroidogenesis may cause disorders of sex development that are recognized in the newborn period as ambiguous genitalia. Some of these disorders, however, will result in a phenotypic female who is unable to synthesize either androgens or oestrogens. These disorders may cause congenital adrenal hyperplasia and include steroidogenic acute regulatory protein (StAR) deficiency and 17-hydroxylase deficiency. Patients with carbohydrate-deficient glycoprotein syndrome produce abnormally glycosylated gonadotropins that are biologically inactive. The disordered puberty is more severe in females than males. Noonan syndrome, caused by a defect of the PTPN11 gene in 50% of individuals, is a constellation of features including short stature, characteristic facies, and right-sided cardiac defects, as well as undescended testes. Although females with Noonan syndrome have normal ovarian function, some males may have abnormal Leydig cell function. Other well-recognized genetic syndromes associated with hypergonadotropic hypogonadism include the fragile X premutation, type 1a pseudohypoparathyroidism (Albright’s hereditary osteodystrophy), blepharophimosis syndrome, myotonic dystrophy, and ataxia-telangiectasia syndrome (36, 37).

The term vanishing testis syndrome refers to the case of the phenotypically normal male born with bilaterally absent testes. Normally-functioning testicular tissue is presumably present in early gestation, as the external and internal genitalia are normally formed and there are typically no müllerian remnants, implying normal secretion of testosterone and MIS in utero. This condition is thought to be due to antenatal bilateral torsion of the testes or other vascular events. This condition is uncommon, occurring in approximately 1:20 000 males. Careful physical examinations at birth and during childhood will reveal apparent bilateral undescended testes, and further evaluation by measuring MIS, inhibin b, or human chorionic gonadotropin (hCG)-stimulated testosterone will show the absence of functioning testicular tissue. However, if a good physical examination is not performed in childhood, this condition may remain undetected and present with delayed pubertal development. In some cases, the vascular insult may occur near the time of delivery, and bilateral testicular necrosis may be identified (38).

Viral orchitis is an uncommon problem that usually affects adult men. Infection with the mumps virus causes orchitis in 15–30% of postpubertal males, although orchitis is rare in children. In 15–30% of cases, orchitis is bilateral. Symptoms include pain, oedema, and erythema of the scrotum. After resolution, approximately half of affected men have decreases in testicular volume. Some patients will have minor alterations in endocrine function, but sterility is rare. In women, mumps oophoritis is less common, affecting 5% of infected adult women. Mumps oophoritis is very rare in childhood, and rarely causes alterations of endocrine function or fertility in any affected female (39).

Other causes of orchitis and oophoritis include bacterial infections with Chlamydia trachomatis, Neisseria gonnorhea, and Escherichia coli; other viral pathogens such as coxsackie virus and varicella; and noninfectious causes, such as Henoch–Schonlein purpura and other vasculitides.

Autoimmune oophoritis (AO) presents as premature ovarian failure or less commonly as absent puberty, arrested puberty, or primary amenorrhoea. It is estimated that 1–5% of women with premature ovarian failure have ovarian autoimmunity. AO is commonly reported in type 1 autoimmune polyglandular syndrome (APS), and may be less often found in type 2 APS. It is nearly always associated with autoimmune adrenalitis and, if primary adrenal insufficiency is documented, approximately 20% of females will have AO. In the setting of type 1 APS, 36% of females will have AO, and 4% of males will have autoimmune orchitis. Affected individuals will have clinical ovarian failure and elevations of both LH and FSH. Antibodies to several cytochrome P450 steroidogenic antibodies have been documented in patients with AO, but assays for these autoantibodies are not commonly available. However, because of the close association between autoimmune adrenalitis and AO, anti-adrenal antibodies directed against the 21-alpha-hydroxylase enzyme may serve as a surrogate marker in the patient with clinical ovarian failure. Because primordial follicles are preserved early in the course of AO, treatment with immunosuppressive agents such as glucocorticoids may be effective (37, 40).

Gonadal tissue is very radiosensitive. Germ cells are particularly prone to radiation injury. In the male, loss of germ cells leads to infertility, but Leydig cells are more resistant to radiation-induced damage. Hence, at lower doses of radiation, there may be loss of fertility with preservation of endocrine function, diagnosed by elevation of FSH with normal LH and testosterone levels. At higher doses of radiation, both fertility and hormone secretion are affected, with elevation of both FSH and LH, and low testosterone concentration. With any degree of radiation exposure in the male child or adolescent, germ cell loss can occur, while Leydig cell injury does not usually occur until doses exceed 20–30 Gy. This situation contrasts with females, in whom germ cell loss is closely tied to loss of endocrine function due to loss of follicle development. The number of oocytes in the female is limited, and exposure later in adolescence or in adulthood, when there are normally fewer oocytes present, is associated with worse endocrine and reproductive outcomes than exposure early in childhood, when the number of oocytes present is larger. Radiation exposure in doses above 10 Gy in pubertal girls is associated with adverse reproductive outcomes, while doses above 15 Gy place prepubertal girls at risk.

Oophoropexy, which refers to surgical relocation of the ovaries, may move at risk ovaries out of the field of radiation, but results in loss of spontaneous fertility and may make assisted reproductive techniques more difficult. Although freezing embryos is an accepted technique for preserving fertility in adults, this is not usually an option for the paediatric patient. Other techniques, such as oocyte cryopreservation or ovarian tissue cryopreservation, are being studied, but are not widely available. For male adolescents undergoing radiation therapy, semen samples may be frozen, and this should be offered to all those at risk (41).

Chemotherapeutic medications, especially alkylating agents, commonly cause gonadal injury in both prepubertal and pubertal patients. Higher dose protocols are more likely to cause gonadal dysfunction. This group of medications includes cyclophosphamide, ifosfamide, procarbazine, busulfan, chlorambucil, and others. Similar to the case of radiation exposure, females are at higher risk for chemotherapy-induced fertility and hormonal sequelae, while defects of testosterone secretion in males exposed to alkylating agents are uncommon. Overall, males who have survived cancer in childhood have a 24% decrease in fertility, while females have a 10-fold increase in the incidence of premature ovarian failure (41). Similar to radiation exposure, the feasibility of cryopreservation of semen should be discussed with adolescent males and their families, whether it is obtained from an ejaculate or by extraction from the testicle. Techniques capable of preserving fertility in female children and adolescents are considered experimental at this time.

Diagnostic algorithms for the evaluation of delayed puberty and possible hypogonadism are presented in Fig. 7.2.9.3 and Fig. 7.2.9.4, and Table 7.2.9.3. The evaluation starts with a careful history and physical examination. Important historical features include the presence or absence of any signs of puberty, including the age at onset and the tempo of progression. Inquiry about the patient’s sense of smell is important, because patients and families will not volunteer this information in this setting. The growth pattern of the patient must be assessed by examination of a standard growth chart. Finally, the timing of puberty in the parents, siblings, and other relatives is critical, as many of the possible conditions are heritable.

Important physical features include the patient’s height and weight, the presence or absence of any signs of puberty, and the quantification of these signs if possible. Quantification of pubertal development includes assessment of Tanner stages, measurement of testicular volume and penile length in males, and measurement of breast size in females or gynecomastia in males.

The laboratory diagnosis begins with determinations of LH and FSH concentrations. Normal or low gonadotropin levels direct the evaluation along the hypogonadotropic hypogonadism pathway, while elevations of gonadotropins suggest a diagnosis involving primary testicular or ovarian failure.

The principal goal of treatment of delayed or absent puberty is the attainment of sex steroid levels and physical development that are appropriate for the stage of adolescent development. Replacement may be temporary in cases of transient delayed puberty, such as constitutional delay of growth and puberty (CDGP), or long-term in cases of permanent absence of pubertal development. Subsequent goals of sex steroid therapy in the adolescent are to promote physiological linear growth and development of secondary sexual characteristics, and to permit the acquisition of normal body composition, including muscle mass and skeletal bone mineral content, with the purpose of mimicking the normal physiologic process. Regardless of whether the patient has hyper- or hypogonadotropic hypogonadism, long-term sex steroid replacement is accomplished similarly.

Agents presently available for androgen replacement are listed in Table 7.2.9.4. Not all of the preparations are universally available, and few are suggested for the induction of puberty, mainly because the dosage forms are metered to full androgen replacement therapy for the adult. As most are drug delivery devices, they cannot be easily altered to deliver the small, and then increasing doses of testosterone required to permit normal pubertal development in hypogonadal adolescents, or in those with CDGP.

The oral 17α-hydroxylated preparations are virtually never used because of the concern of liver toxicity and there is very little experience in adolescents with the buccal formulations. Testosterone undecanoate is not considered hepatotoxic. Unmodified testosterone, taken orally, is rapidly inactivated by first-pass hepatic metabolism.

Oxandrolone is a nonaromatizable, non5-α reducible oral steroid hormone, which interacts directly with the androgen receptor. It augments growth velocity in boys with CDGP without disproportionate advancement of skeletal maturation, which would theoretically decrease adult height (42). In prepubertal boys, a marked increase in body mass index, a decrease in the triceps and subscapular skinfolds, and an increase in the upper body muscle area have been noted following oxandrolone, 2.5 mg/day (43). At that dose, oxandrolone was an anabolic steroid without significant virilizing action.

The primary clinical uses for androgen therapy in adolescent males are to induce pubertal development, and as replacement therapy in those with permanent hypogonadism of either the hypogonadotropic or hypergonadotropic variety. The most common cause, although its precise incidence is unknown, is CDGP.

Without intervention, most patients with CDGP will undergo normal pubertal development spontaneously and most, but not all, will reach their genetically determined mid-parental height range (44). Many adolescents suffer significant emotional distress because they differ in their appearance from their peers during these years. Androgen therapy was initially proposed for boys with CDGP to alleviate their psychological discomfort, in addition to the beneficial effects on bone mineral accrual, lean body mass (protein metabolism), and the regional distribution of body fat.

The authors recognize that the majority of boys who have sought subspecialist evaluation are anxious to begin androgen therapy, and are generally pleased with the results, albeit subtle, even after 3 months of therapy with 50–75 mg long-acting esters per month. Their reasons to begin therapy fall into the appearance (too young), social (not considered a peer), and athletic (cannot compete because of size and lack of strength) spheres. The dose is increased by 25–50 mg/month every 3 months if spontaneous pubertal development has not occurred. This may be assessed by an increase in testicular size, indicating gonadotropin release despite the negative feedback effects of the exogenous testosterone, or by rising early morning levels of testosterone obtained at least 3 weeks following the previous testosterone injection. Therapy is discontinued when the testicular volume is approximately 10 ml. The longest acting ester available is the undecanoate, and because of its approximately 3-month duration of action, it is not appropriate for adolescents with presumed CDGP.

For those with permanent hypogonadism, the escalation of the cypionate or enanthate continues until a dose of approximately 150 mg monthly is reached, after which consideration may be given to switching to twice monthly at 100 mg each administration, or increasing to a maximum of 200 mg twice monthly, which is the adult dose. At about the time of moving to twice monthly injections, one might consider the cutaneous gel, which is available in sachet packages of 2.5 and 5 g or metered pump dispensing 1.25 g, which we consider a mid-pubertal dose. The advantage of the gel is that the levels of testosterone, dihydrotestosterone (DHT), and oestradiol are all within the physiological range for the entire day. Subsequent alterations in dose can be made by measuring the circulating level of testosterone. Those receiving intramuscular testosterone have higher than normal levels of T, DHT, and oestradiol for part of the interval and lower than normal for the latter part of the interval.

Puberty can be induced using an oestrogen started at approximately 12 years, an age appropriate to induce breast development without affecting the rate of bone maturation or growth potential (45). The initial dose should be low, one-sixth to one-quarter of the adult dose (Table 7.2.9.5), and increased gradually at intervals of 3–6 months. The administration of very low-dose depot oestradiol (initial dose of 0.2 mg/month, im) permitted relatively age-appropriate (12–13 years of age) feminization without interfering with the effect of growth hormone on the enhancement of height potential (46).

In a study of girls with Turner's syndrome, 56 subjects who were receiving rhGH therapy received low dose, oral micronized oestradiol (5 µg/kg per day) for 2 years followed by 1 year at 7.5 µg/kg per day and then 10 µg/kg per day (47). The main purpose of the study was to induce feminization as close to physiologically as practicable without negatively affecting adult height. The majority had similar breast development and progression compared to a population of Dutch girls, but approximately 2 years delayed. As previously reported, adult uterine size was not attained, likely due to the 45,X karyotype and not due to the protocol for the escalation of the oestradiol dose. No direct comparison with the transdermal application of oestradiol (see below) was made.

Transdermal oestradiol patches have been used with some advantages over the traditional oral administration of oestradiol or one of its synthetic analogues. Nocturnal application (3.1–12.5 µg/day of 17 β-oestradiol) in girls with hyper- or hypogonadotropic hypogonadism produced levels of oestradiol that were similar to those measured in girls during spontaneous adolescent development (48). Cutaneous administration of oestradiol in hydroalcoholic gel is another therapeutic possibility that can be used to induce puberty.

In general, the dose of oestrogen can be increased every 6–12 months to reach the full replacement dose after 2 or 3 years of therapy. Replacement therapy in most patients eventually involves cyclic oestrogen–progesterone therapy. Once full oestrogen replacement has been reached, cyclical progesterone (5–10 mg of medroxyprogesterone acetate) can be added every month to induce monthly menstrual bleeding. Once full pubertal development has been reached, the oestrogen dosage should be the minimum that will maintain normal menstrual periods, prevent calcium loss from bone, and permit the accrual of peak bone mass early in the third decade. At that time, low dose birth control pills are an alternative option; however, by definition the dose of oestrogen is greater than the physiological dose for an adult woman.