congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) is a group of inherited conditions in which a person is born with a faulty enzyme in the adrenal steroid-making pathway. Picture an assembly line with one broken station: the product that should be made downstream runs short, while the raw materials waiting at the blockage pile up and get diverted into a different product. The result is a characteristic shift in which adrenal hormones the gland can and cannot make.

By far the most common form is 21-hydroxylase deficiency. The broken enzyme means the gland cannot make enough cortisol (and often aldosterone), so the pituitary, sensing low cortisol, ramps up ACTH. The relentless ACTH drive makes the adrenal glands overgrow — the hyperplasia in the name — and pushes the backed-up precursors into the androgen pathway, causing androgen excess.

The clinical picture depends on how severe the enzyme defect is. The severe classic form can present in newborns with ambiguous genitalia in genetic females and, in the salt-wasting type, a dangerous adrenal crisis with low sodium and high potassium in the first weeks of life. Milder non-classic forms may surface later as early puberty, excess hair, acne, or menstrual irregularity. Treatment replaces the missing glucocorticoid (and mineralocorticoid when needed), which also calms the excess ACTH and androgen drive.