Characterization Of The Novel Misssense Mutation G250V In Type II 3beta-Hydroxysteroid Dehydrogenase (3beta-HSD2) Gene Found In A 46,XX (Female) Patient With Congenital Adrenal Hyperplasia (CAH)

BAQUEDANO MARIA SONIA; CIACCIO, M; MARINO, R; PEREZ GARRIDO, N; RAMIREZ, P; RIVAROLA, M; BELGOROSKY, A

Houston, Texas

Congreso; The Endocrine Society´s 94th Annual Meeting (ENDO 2012); 2012

The Endocrine Society

3betaHSD2 deficiency, a rare form of CAH, is characterized by varying degrees of salt loss and incomplete masculinization in males and mild virilization or normal external genitalia in females. 3betaHSD2 gene mutations have been reported in a small number of affected females. We report a 7-moth-old 46,XX girl who was referred because of premature pubarche and postnatal clitoromegaly. Hormonal profile showed inadequate production of glucocorticoids and very high serum ACTH levels (cortisol:4.8ug/dl:ACTH: 2888pg/ml), increased serum 17OHProg(141ng/ml) and plasma renin levels (423.9ng/ml), in addition to very high levels of DHEAS (53000ng/ml). Genetic analysis revealed a novel homozygous c.749G>T mutation in 3betaHSD2 gene, resulting in a G250V change. This G is highly conserved in the vertebrate 3betaHSD2 gene family and is located in the substrate-binding domain of the enzyme. As in silicoPolyPhen and SIFT analysis predicted G250V to be a damaging substitution, enzymatic activity was analyzed by in vitro analysis of mutant recombinant enzyme generated by site-directed mutagenesis after its transient expression in COS cells. Enzyme activity using 0.5 uM pregnenolone as substrate in the medium after 6h revealed relative conversion rates of pregnenolone to progesterone of 78+/-4% and 21+/-% by WT and G250V-3betaHSD2 enzymes respectively. Using 0.5 uM dehydroepiandrosterone as substrate, the relative conversion rate of dehydroepiandrosterone to androstenedione after 6h was 87+/-% and 23+/-% by WT and G250V3beta- HSD2 enzymes, respectively. Immunofluorescence studies showed that both WT and mutant G250V-3betaHSD2 protein colocalized with endoplasmic reticulum. We identified a novel G250V 3betaHSD2 gene mutation which causes an incomplete loss of enzymatic activity, explaining the compensated non-salt loss phenotype of CAH. Peripheral type 1, 3betaHSD activity often complicates the hormonal diagnosis of this disorder. However, the discrepancy between the grossly elevated 17-OHP levels, as well as very high levels of DHEAS and the lack of ambiguous genitalia point against 21-hydroxylase deficiency. Flux via the adrenal backdoor pathway, which convert 17OHProg to dihydrotestosterone (DHT) has been recently implicated in human disorders of androgen excess. We hypothesized that this alternate pathway could not be activated in 3betaHSD2 deficiency due to very low intraadrenal 17OHProg substrate levels, explaining mild virilization or even normal sexual differentiation in females.