- In girls, the first sign of puberty is the onset of breast development (thelarche). Breast enlargement is followed by the development of pubic hair (pubarche). Menarche occurs 2–3 years after the onset of puberty. The first 1–2 years following men-arche involve anovulatory cycles associated with irregular and usually painful periods. Peak growth velocity (the growth spurt) occurs within the first year after the onset of puberty.
- In boys, the first sign of puberty is an increase in testicular volume (≥ 4 mL). Testicular enlargement is followed by penile and pubic hair development. Spermatogenesis begins at Tanner stage 3 (see below). Peak growth velocity occurs 2 years after the onset of puberty (Tanner stage 3–4, at a testicular volume of about 12 mL). Boys experience a greater peak height velocity than girls.
In both sexes, puberty progresses through distinct stages in an orderly and consistent manner.
Delayed puberty
Delayed puberty is defined as the absence or incomplete development of secondary sexual characteristics by an age at which 95% of children of that sex and culture have initiated sexual maturation.
- In boys, delayed puberty may be diagnosed when there is no testicular enlargement by age 14.
- In girls, delayed puberty may be diagnosed when there is no breast development by age 13.
Aetiology
Causes of delayed puberty are summarized in Box 29.2..
Constitutional delay of growth and puberty
Constitutional delay of growth and puberty (CDGP) is one of the most common conditions presenting to paediatric endocrinologists. It is a normal variant of growth and puberty, and is characterized by a delayed onset of puberty, pubertal growth spurt and skeletal maturation (i.e. delayed bone age).
In the years preceding the expected time of puberty, the growth pattern of these children is normal (usually along the lower growth percentiles). The height of the child begins to drift from the growth curve because the onset of the pubertal growth spurt is delayed. However, the child’s height is appropriate for the bone age. Physical examination and biochemical investigations are normal and prepubertal.
Patients often have a family history of a late onset of puberty in one or both parents. The predicted height for the child is in the appropriate range for the parental heights. It may be difficult to distinguish between CDGP and congenital GnRH deficiency as gonadotrophin levels are low in both conditions, and the diagnosis may only be made with time and serial observations. Persistent hypogonadism beyond age 18 is highly suggestive of congenital GnRH deficiency.
Hypogonadotrophic hypogonadism
Hypogonadotrophic (or secondary) hypogonadism is due to an impaired secretion of hypothalamic GnRH and/or impaired FSH and LH levels. Hypogonadotrophic hypogonadism may be acquired or congenital (see Box 29.2).
Congenital hypogonadotrophic hypogonadism may be associated with the following:
- Anosmia: in Kallmann’s syndrome, which is usually X-linked (although autosomal dominant transmission can also occur). Kallmann’s syndrome may be due to the sporadic or familial mutations of several genes (e.g. KAL1, FGFR1 [KAL2], PROK2) encoding cell surface adhesion molecules or their receptors required for the migration of GnRH-secreting neurones into the brain and hypothalamus. Kallmann’s syndrome may be associated with midline facial abnormalities (e.g. cleft palate), red–green colour blindness, hearing loss, urogenital tract abnormalities and synkinesis (mirror movements of the hands).
- Mental retardation and obesity: in Prader–Willi syndrome (caused by deletion of part of paternally derived chromosome 15q) and Laurence–Moon–Biedl syndrome (also associated with polydactyly and retinitis pigmentosa).
- Congenital adrenal hypoplasia: due to a mutation of the NROB1 (DAX-1) gene.
Hypogonadotrophic hypogonadism
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