Quantitative evaluation of partial deletions of the DAZ gene cluster

Abstract

Partial deletions of the DAZ gene cluster are thought to cause spermatogenesis impairment. The presence of homologous copies of this gene in the Y chromosome does not allow PCR to be used for the identification of this abnormality. Hence, sequence family variants (SFV), following amplification of sY581, sY587 and sY586 and subsequent enzymatic digestion with Sau3A, DraI and TaqI, respectively, and the dual fiber fluorescence in situ hybridization (FISH) have been used to this aim. However, SFV is not always able to identify single DAZ gene copy deletions. We report a quantitative real-time PCR application to evaluate partial deletions of the DAZ gene cluster. To accomplish this, we designed a probe on exon 6 of the DAZ gene which is repeated 3 times in DAZ1, once in DAZ2 and DAZ3 and twice in DAZ4. Five normozoospermic healthy men (C1-C5) having 4 DAZ gene copies by SFV were selected. Fiber-FISH confirmed this outcome in C1-C4, but not in C5 who had an incomplete DAZ gene cluster. The men underwent then quantitative real-time PCR and C1 was arbitrarily selected as calibrator for the calculation of the DAZ gene signals because of the lowest variation in the threshold cycles. Real-time PCR identified 7.2+/-0.05 signals in C2-C4 and 5.4+/-0.05 signals in C5. The overall coefficient of variation was 1.4+/-0.2%. The loss of two signals in this subject may relate to a deletion of both DAZ2 and DAZ3 or of DAZ4 gene. Since SFV showed clearly the presence of DAZ2, it may be hypothesized that C5 lacks DAZ4. In conclusion, these data suggested that quantitative real-time PCR seems to be an effective and reproducible technique that can be used to study the DAZ gene cluster. In addition, the probe chosen for this approach may give indication on the DAZ gene copy deleted.