SRD5A2 gene analysis in an Italian population of under-masculinized 46,XY subjects

The differential diagnosis of male under-masculinization, including a wide spectrum of phenotypes and a heterogeneous genetic basis, is crucial for the correct management of the patients. To characterize an Italian population of under-masculinized males, we performed the molecular analysis of the SRD5A2 gene (2p23), encoding the 5alpha-reductase-2 enzyme that converts testosterone (T) to dihydrotestosterone (DHT), and is required for full masculinization of the male foetus.

Twenty-six Italian patients with 46,XY kariotype and various degrees of ambiguous genitalia were retrospectively selected for this study. Twelve of these patients, 10 of whom were referred for partial androgen insensitivity syndrome (PAIS), were raised as females; 15 were raised as males and all had a severe hypospadias. For most of the patients, the case histories and hormonal findings were incomplete but all could be included in the clinical characteristics of under-masculinization.

For hormonal evaluation, T and DHT were measured by means of radioimmunoassay (RIA) and high-performance liquid chromatography (HPLC)-RIA methods, respectively. Genomic DNA of all patients and relatives was extracted from peripheral blood, the five exons of the SRD5A2 gene were amplified by polymerase chain reaction (PCR) and submitted to automatic sequencing.

Five known mutations affecting the NADPH binding function and one new mutation affecting the enzyme C-terminus were identified in a total of eight patients (two of whom were sisters). Five families were characterized, and in two patients only one affected allele was observed. The extension of the analysis to the regions flanking exons allowed the identification of a new polymorphism in intron 2, whose frequency was determined.

This first report of an Italian population underlines the importance of differential diagnoses in patients with under-masculinization. The lack of precise genotype-phenotype correlation in some of the mutations highlights the necessity to improve knowledge about the biochemical aspects of steroid 5alpha-reductase action and about the interactions of genetic and environmental factors.