GROWTH, PUBERTY AND SEXUAL DIFFERENTIATION
Postnatal linear growth may be divided into three phases: infancy, childhood and puberty (Figure 24.1). In infancy and childhood, linear growth is rapid although height velocity decreases. Hormonal influences on growth predominate, particularly the GH–IGF-1 axis. The pubertal growth spurt, which starts roughly 2 years earlier in girls than boys, arises as a result of increased sex steroid in addition to GH production. In girls, this coincides with the start of breast development (thelarche), reaches a peak height velocity at around age 12, and is followed by the onset of menarche (the first menstrual cycle) before declining. In contrast, the pubertal growth spurt in boys does not occur until puberty is well advanced (when testicular volumes are 10–12 mL). Males are thus on average 13–14 cm taller than females as a result of 2 additional years of pre-pubertal growth and a greater pubertal height velocity.
Puberty normally occurs between the ages of 8 and 13 years in girls, and 9 and 14 years in boys. In girls, puberty begins with breast enlargement at an average age of 11. This is followed by pubic and axillary hair development (adrenarche), and the start of periods (menarche), which occurs at a mean age of 13.5 years. In boys, puberty begins with testicular enlargement (attainment of 4 mL testicular volume) at a mean age of 12 years, and is followed by pubic and axillary hair growth (Figure 24.2).
This is arbitrarily defined as a height which is 2 standard deviations below the mean for the child’s age and gender. Assessment of the genetic contribution to stature is made by calculation of the target height centile range using parental height. Most children with short stature do not have an underlying condition and will not require further investigation. A thorough history, examination and clinical evaluation, including accurate serial plotting of height on growth charts (auxology) for assessment of height velocity, will determine which children need investigation (Figure 24.3). Causes of short stature include:
• Familial. The most common cause. The height standard devia-tion score will lie within target height.
• Constitutional delay of growth and puberty (CDGP). A vari-ant of normal and more common in boys than girls. There is often a family history of delayed puberty.
• Chronic disease (e.g. renal failure).
• Dysmorphic syndromes (e.g. Turner’s syndrome; Chapter 25) and Prader–Willi syndrome.
• Endocrine disorders (e.g. growth hormone deficiency – mostly idiopathic – hypothyroidism or Cushing’s syndrome).
This is defined as the onset of puberty before age 8 in girls or age 9 in boys. Gonadotrophin-dependent precocious puberty (GDPP) refers to the development of secondary sexual characteristics in the normal sequence as a result of hypothalamic activation occurring early. Gonadotrophin-independent precocious puberty (GIPP) occurs as a result of abnormal sex steroid production, is independent of hypothalamicâ€“pituitary activation, and can result in non-consonant puberty (puberty occurring in an abnormal sequence).
• GDPP is more common in girls and is usually idiopathic. Treatment with a GnRH analogue can be considered.
• GIPP is rare and pathological causes (such as congenital adrenal hyperplasia, adrenal tumours or sex steroid-producing tumours) are more common.
This is defined as the absence of secondary sexual characteristics by age 13 in girls or age 14 in boys. Causes can be divided into:
• Hypogonadotrophic hypogonadism (inappropriately low gonadotrophins) for example resulting from CDGP. Treatment for CDGP, in the form of testosterone for boys or oestrogen for girls, is considered if there is an effect on psychological well-being.
• Hypergonadotrophic hypogonadism (inappropriately high gonadotrophins) for example resulting from chromosomal abnormalities (Turner’s syndrome, Klinefelter’s syndrome; Chapter 28) or acquired gonadal failure (prior radiotherapy or chemotherapy).
The term disorders of sex development (DSD) is used to describe congenital conditions in which the development of chromosomal, gonadal or anatomical sex is atypical. The causes are described clinically as masculinised females, under-masculinised males, or true hermaphrotidism. The most common cause of ambiguous genitalia is congenital adrenal hyperplasia from 21-hydroxylase deficiency (see Chapter 26), leading to a masculinised female. The management of DSD, including gender assignment, is complex and should involve an experienced multidisciplinary team comprising a paediatric endocrinologist, paediatric urologist and psychologist.
Transition of young people into the adult service
This is a planned process that addresses the medical, educational and psychosocial needs of young people with chronic conditions as they move into adulthood. Transition clinics, involving joint input by paediatric and adult endocrine teams, improve continuity of care, enable better disease control, minimise the drop-out rate from follow-up and help patients’ acceptance of adult services. Increasing emphasis is placed on education and self-management of their condition.