Deciphering balanced translocations in infertile males by next-generation sequencing to identify candidate genes for spermatogenesis disorders

Male infertility affects about 7% of the general male population. Balanced structural chromosomal rearrangements are observed in 0.4-1.4% of infertile males and are considered as a well-established cause of infertility. However, underlying pathophysiological mechanisms still need to be clarified. A strategy combining standard and high throughput cytogenetic and molecular technologies was applied in order to identify the candidate genes that might be implicated in the spermatogenesis defect in three male carriers of different balanced translocations. Fluorescence in situ hybridization (FISH) and whole-genome paired-end sequencing were used to characterize translocation breakpoints at the molecular level while exome sequencing was performed in order to exclude the presence of any molecular event independent from the chromosomal rearrangement in the patients. All translocation breakpoints were characterized in the three patients. We identified four variants: a position effect on LACTB2 gene in Patient 1, a heterozygous CTDP1 gene disruption in Patient 2, two single-nucleotide variations (SNVs) in DNAHS gene and a heterozygous 17q12 deletion in Patient 3. The variants identified in this study need further validation to assess their roles in male infertility. This study shows that beside the mechanical effect of structural rearrangement on meiosis, breakpoints could result in additional alterations such as gene disruption or position effect. Moreover, additional SNVs or copy number variations may be fortuitously present and could explain the variable impact of chromosomal rearrangements on spermatogenesis. In conclusion, this study confirms the relevance of combining different cytogenetic and molecular techniques to investigate patients with spermatogenesis disorders and structural rearrangements on genomic scale.

Automated summary

Male infertility affects about 7% of the male population, with balanced chromosomal rearrangements being a well-established cause but with unclear underlying pathophysiological mechanisms. This study used a combination of cytogenetic and molecular techniques to identify candidate genes implicated in spermatogenesis defects in three male carriers of different balanced translocations. Breakpoints were characterized at the molecular level, revealing gene disruptions and variations that need further validation for their roles in male infertility. This study emphasizes the importance of combining cytogenetic and molecular techniques to investigate spermatogenesis disorders in patients with structural rearrangements on a genomic scale.