Congenital adrenal hyperplasia is due to 21-hydroxylase deficiency in > 90% of cases. This is a very common
genetic disorder for which biochemical screening is now performed. The classical form occurs in 1:15,000–16,000
live births, while the nonclassical form occurs in 1:1000. Congenital adrenal hyperplasia is the most common cause
of primary adrenal insufficiency in childhood. Undertreatment of the condition leads to acute risk of adrenal crisis and to long-term risk of short adult stature and infertility, whereas overtreatment is associated with short stature, obesity and other effects of hypercortisolism, including, but not limited to, osteoporosis.