CYP21A2

About CYP21A2

CYP21A2 on chromosome 6p21.33, within the HLA region, encodes steroid 21 hydroxylase, an adrenal enzyme required to make cortisol and aldosterone. Deficiency of this enzyme causes the large majority of cases of congenital adrenal hyperplasia, an autosomal recessive disorder in which low cortisol drives increased ACTH, enlarging the adrenal glands and diverting steroid precursors toward androgens. The classic salt wasting form can cause a life threatening adrenal crisis in newborns, and newborn screening for it is performed in many countries. Excess androgens can cause atypical genital development in newborns with XX chromosomes and early puberty in children of both sexes, while non classic forms present later, often with features resembling polycystic ovary syndrome. Genetic testing is complicated by a neighboring pseudogene, CYP21A1P, from which many disease variants are copied by gene conversion.