CYB5A and hyperinsulinemic hypoglycemia, familial, 4: Therefore, isolated 17,20-lyase deficiency is a syndrome, which may be caused by specific mutations in the CYP17A1 (p.R347H, p.R347C, p.R358Q, and p.E305G), POR (p.G539R), and CYB5A (p.W27X and p.H44L) (14).