Abstract
Steroid 11 beta hydroxylase deficiency (11 beta-OHD) (OMIM #202010) is the second most common form of congenital adrenal hyperplasia (CAH), accounting for 5-8% of all cases. It is an autosomal recessive enzyme defect impairing the biosynthesis of cortisol. The CYP11B1 gene encoding this enzyme is located on chromosome 8q22, approximately 40 kb from the highly homologous CYP11B2 gene encoding for the aldosterone synthase. Virilization and hypertension are the main clinical characteristics of this disease.
In Tunisia, the incidence of 11 beta-OHD appears higher due to a high rate of consanguinity (17.5% of congenital adrenal hyperplasia). The identical presentation of genital ambiguity (females) and pseudo-precocious puberty (males) can lead to misdiagnosis with 21 hydroxylase deficiency. The clinical hallmark of 1113 hydroxylase deficiency is variable, and biochemical identification of elevated precursor metabolites is not usually available.
In order to clarify the underlying mechanism causing 11 beta-OHD, we performed the molecular genetic analysis of the CYP11B1 gene in a female patient diagnosed as classical 11 beta-OHD. The nucleotide sequence of the patient's CYP11B1 revealed two novel mutations in exon 4: a missense mutation that converts codon ACT (serine) to ATT (isoleucine) (c.650G>T; p.S217I) combined with an insertion of a thymine at the c.652-653 position (c.652_653insT). This insertion leads to a reading frame shift, multiple incorrect codons, and a premature stop in codon 258, that drastically affects normal protein function leading to a severe phenotype with ambiguous genitalia of congenital adrenal hyperplasia due to 11 beta hydroxylase deficiency. (C) 2011 Elsevier Inc. All rights reserved.