GROWTH, PUBERTY AND SEXUAL DIFFERENTIATION
Normal growth
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.
Normal puberty
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).
Short stature
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).
Precocious puberty
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 hypothalamic–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.
Delayed puberty
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).
Sexual differentiation
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.
