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3 beta hydroxysteroid dehydrogenase autoantibodies in patients with idiopathic premature ovarian failure target N- and C-terminal epitopes.

The steroid cell enzyme 3 beta hydroxysteroid dehydrogenase (3 beta HSD) has been identified as a target of steroid cell autoantibodies, and autoantibodies to this enzyme are present in patients with premature ovarian failure and patients with autoimmune polyendocrine syndrome 1. The aim of the present study was to develop a radioligand binding assay for 3 beta HSD autoantibodies and to exploit this to examine regions of the molecule targeted by autoantibodies. We generated a construct of 3 beta HSD coupled to a luciferase fusion partner in order to maximize the yield of (35)S-radiolabeled protein. Labeled 3 beta HSD was then immunoprecipitated and the autoantibodies quantified by phosphoimaging. Autoantibodies to 3 beta HSD were detected in 12 of 100 (12%) idiopathic premature ovarian failure patients and 0 of 103 (0%) healthy age-matched controls (P < 0.0001). Three overlapping fragments of 3 beta HSD cDNA were cloned downstream of luciferase to examine autoantibody binding sites. Two of nine sera with 3 beta HSD autoantibodies (22%) displayed reactivity to the N terminus of 3 beta HSD, and seven (77%) showed reactivity to the C terminal; no sera reacted with the middle region. Our study demonstrates a markedly enhanced disease specificity of autoantibodies to 3 beta HSD detected using this novel assay and shows that distinct regions of the molecule are targeted.