THE SIGNIFICANCE OF DISTURBANCES IN DNA DOUBLE-STRAND BREAK FORMATION AND REPAIR IN NON-OBSTRUCTIVE AZOOSPERMIA PATIENTS

Abstract

Objective

The ultimate treatment management of NOA involves testicular sperm extraction; however, in almost half of the men with NOA, no sperm can be retrieved. DNA defects such as double-strand breaks (DSBs) can disturb meiotic recombination and cause infertility in men due to complete early meiotic arrest. To date, few genes participating in DSB formation and/or repair have been associated with infertility in humans. However, the relationship between the failure of the meiotic DSB process and human infertility remains poorly understood. We aim to identify new genetic causes responsible for the nonobstructive azoospermia (NOA) with meiotic arrest by using exome sequencing

Materials and Methods

This case-control study was conducted on two Turkish consanguineous families, comprising infertile men with NOA. Testicular histopathology results showed meiotic arrest at the spermatid stage. Karyotypes were normal and no Y chromosome microdeletion was detected in the affected men. Ethical approval was obtained from the Comité de Protection de la Personne (CPP) of Strasbourg University Hospital.Saliva samples from index cases and both parents were collected after obtaining written informed consent. Exome sequencing was performed using the GenomEast Platform (IGBMC, Strasbourg, France). Detected variants were annotated and ranked by VaRank (v1.4.3).

Results

Exome sequencing revealed homozygous pathogenic variations in two genes namely C11orf80 (also known as TOPBBL) and RAD51AP2. The first gene is related to meiotic DNA DSB formation, while the latter is associated with DSB repair in the respective families. Meiosis could not be completed in either situation, resulting in spermatogenesis arrests at the pachytene stage of meiosis 1. Two recent reports described four NOA men from two families presenting homozygous truncating variants in C11orf80. Similarly, homozygous or compound heterozygous loss-of-function variations in RAD51AP2 were previously identified in four men diagnosed with idiopathic NOA. Since the identification of both genes were after the latest systematic review, they were neither scored norvalidated for the male infertility. The gene-disease relationship (GDR) was evaluated by including published patients and variants as well as results from the actual study. C11orf80 and RAD51AP2 were scored as 13 and 14 respectively with a classification of “strong” for both genes.

Conclusion

Our findings support the role of C11orf80 and RAD51AP2 as genetic contributors to human infertility by causing meiotic arrest during spermatogenesis in men.

Discussion

The main limitation of our study is the small number of cases included. However, it provides fresh data regarding on NOA phenotypes associated with meiotic arrest. For men with a similar phenotype, genetic screening for C11orf80 and RAD51AP2 could be recommended, and the identification of pathogenic variations might help to avoid unsuccessful testicular biopsy procedures.