The human 3β-hydroxysteroid dehydrogenase (3β-HSD) gene cluster on chromosome 1p13 contains a presumptive pseudogene; 3β-HSD and CYP17 do not segregate with dominantly inherited hirsutism

in Journal of Molecular Endocrinology
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ABSTRACT

Four hirsute females from a family exhibiting idiopathic dominant hirsutism were examined. Basal blood levels of Δ5 and Δ4 steroids were within the normal range, but ACTH stimulation led to increases in 17-hydroxypregnenolone and dehydroepiandrosterone that were significantly above control levels. Using polymorphic genetic markers, the genes for cytochrome P450c17 encoded by CYP17, and the type I and II forms of 3β-hydroxysteroid dehydrogenase (3β-HSD) were found not to segregate with hirsutism in this family, though a base substitution was detected in the 3′ end of exon 1 of the gene for 3β-HSD type I in three of the four patients investigated.

Analysis of PCR amplification products by denaturing gradient gel electrophoresis (DGGE) and sequencing revealed a novel homologue of exon 3 of 3β-HSD. DNA of one of the affected patients was used to create a genomic library in λ gem11 and clones containing the novel homologue were obtained and partially sequenced. The equivalent clone was obtained from a genomic library of an unrelated normal individual. The sequences of the clones from patient and control were identical and homologous to exons 2–4 of human 3β-HSD types I and II. No difference was found in the PCR primer sites that flanked the exon 3 homologue which led to its detection on DGGE gels. In both clones, stop codons and deletions were identified in the exon 4 homologue, leading to the deduction that the sequence comes from a pseudogene, which we call 3β-HSD Ψ1. The pseudogene mapped to chromosome 1p13. It was concluded that dominantly inherited idiopathic hirsutism in this rare kindred was not due to deficiencies in 3β-HSD types I, II, or Ψ, or of CYP17.

 

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