Similarly, mutations in P450 oxidoreductase (POR) cause a form of CAH in which both 21-hydroxylase and 17-hydroxylase/17,20 lyase activities are impaired, but the diagnosis is usually first suspected because recessive POR deficiency also causes the Antley-Bixler skeletal malformation syndrome (13). Here, POR is linked to congenital adrenal hyperplasia.