Identification of missense mutations in the SRD5A2 gene from patients withsteroid 5 alpha-reductase 2 deficiency

BACKGROUND AND OBJECTIVE Mutations of the steroid 5 alpha-reductase type 2 (SRD5A2) gene in karyotypic males result in a spectrum of external genitali a phenotypes ranging from complete female to nearly complete male. Here we performed genomic DNA analyses from individuals bearing the enzyme deficien cy in order to detect the molecular abnormalities. PATIENTS Four unrelated 46,XY patients of Mexican origin with ambiguous ext ernal genitalia were studied. A fertile, phenotypically normal male was als o included. MEASUREMENTS Coding sequence abnormalities of the SRD5A2 gene were assessed by exon-specific polymerase chain reaction, single-stranded conformational polymorphism and sequencing analysis. RESULTS Five different missense mutations (two of them novel mutations) wer e identified. Three subjects presented homozygous single base mutations. Th ese were located at exon 2 (G115D), exon 4 (P212R) and exon 5 (R246Q), and such changes have been described previously. The fourth patient was a compo und heterozygote who presented two mutations located in exons 1 and 2. We f ound a hitherto unreported G --> A transition at the second nucleotide of c odon 85 in exon 1 (GGC --> GAC), substituting glycine for aspartic acid (G8 5D). This patient also presented an identical alteration at codon 115 of ex on 2, which was carried by his father (G115D). Finally, in another subject who was included originally as a control, we found a C --> A transversion ( yet undescribed) at codon 245 in exon 5 (S245Y). CONCLUSIONS Four different single base mutations that cause amino acid subs titutions were detected in the steroid 5 alpha-reductase type 2 gene of aff ected individuals. One patient and a normal control had two previously unde scribed mutations. Although in the latter individual we cannot exclude the possibility that the base change is a genetic polymorphism, the molecular s creening of 100 chromosomes suggests strongly that the change at codon 245 does represent a heterozygous mutation. Further studies, including the recr eation of the mutations, will help to reveal the biochemical consequences r esulting from these changes.