Endogenous sex steroids can be produced in two places—the gonad or adrenal gland. The gonad in females primarily makes oestrogen and in males testosterone. A key physiological hallmark of puberty is the development of progressively rising pulsatile gonadotropin production by the pituitary gland. Rising, pulsatile concentrations of luteinising hormone (LH) and follicle-stimulating hormone (FSH) stimulate the ovary and lead to oestrogen production in girls with associated breast development. In boys the same physiological process will stimulate testicular enlargement and lead to rising testosterone levels and associated genital change. The adrenal gland primarily makes androgen rather than oestrogen in girls and boys but is not stimulated by gonadotropins. Adrenal androgen production in girls and boys will result in pubic and axillary hair development and a degree of genital change in boys but, if the above summary applies, there will be little potential for confusion with true gonadotropin-mediated pubertal change because there is no impact on the key hallmarks of pubertal onset—breast development in girls and testicular enlargement in boys.

With this information determining whether a child is in puberty or not should be straightforward. The 5-year-old girl with a history of progressive breast development and rapid growth or the 5-year-old boy with a testicular volume that is 4 mL or above needs a comprehensive clinical, biochemical and radiological assessment. The likely …