Tandem duplication and copy number polymorphism of the SRY gene in patients with sex chromosome anomalies and males exposed to natural background radiation.

Mutations in the SRY gene encompassing the HMG box have been well characterized in gonadal dysgenesis, male infertility and other types of sex chromosome related anomalies (SCRA). However, no information is available on copy number status of this gene under such abnormal conditions. Employing 'Taqman Probe Assay' specific to the SRY gene, we screened 16 DNA samples from patients with SCRA and 36 samples from males exposed to high levels of natural background radiation (HNBR). Patients with SCRA showed 2-16 copies of the SRY gene of which, one, Oxen (49, XYYYY) had eight copies with sequences different from one another. Of the 36 HNBR samples, 12 had one copy whereas 24 harboured 2-8 copies of the SRY gene. A HNBR male 33F had one normal and one mutated copy of this gene. Analysis of 25 DNA samples from blood and semen of normal males showed only one copy of this gene. Despite multiple copies in affected males, fluorescence in-situ hybridization (FISH) with SRY probe detected a single signal on the Y chromosome in HNBR males suggesting its possible localized tandem duplication. Copy number status of the other Y-linked loci is envisaged to augment DNA diagnostics facilitating genetic counselling to affected patients.