A rare CYP21 mutation (p.E431K) induced deactivation of CYP21A2 and resulted in congenital adrenal hyperplasia

Abstract. Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is caused by mutations in the CYP21A2 gene. The residual enzyme activity is strongly associated with the phenotype. We describe a rare case of CAH with a rare CYP21A2 mutation. The patient was a one-year-old Japanese boy. At 16 days old, he was referred to our hospital because of elevated serum 17-OH-progesterone (17-OHP) levels in neonatal screening. The compound heterozygous mutations (IVS2-13 A/C>G, and p.E431K) in CYP21A2 were identified at 2 months old, and we diagnosed non-classical CAH, since he did not have significant physical signs (pigmentation and salt-wasting). However, his body weight decreased, and his serum 17-OHP level (99.5 ng/mL) was elevated at 3 months old. Steroid replacement therapy was started at 3 months old. Our patient's clinical course resembled simple virilizing (SV) CAH, but classification was difficult because the patient showed increased renin activity indicating an aldosterone deficiency, and late onset of symptoms. While the IVS 2-13 A/C>G mutation is common in the classical form of CAH, p.E431K is a rare point mutation. Functional analysis revealed that the residual enzyme activity of p.E431L was 5.08+-2.55% for 17-OHP and 4.12+-2.37% for progesterone, which is consistent with SV CAH. p.E431 is localized in the L-helix near the heme-binding site. The mutation might interfere with heme binding, leading to deactivation of CYP21A2. This report showed that CYP21A2 p.E431 has an important effect on enzyme activity.