Whole-exome sequencing improves the diagnosis and care of men with non-obstructive azoospermia

Abstract

Non-obstructive azoospermia (NOA) is a severe and frequent cause of male infertility, often treated by testicular sperm extraction followed by intracytoplasmic sperm injection. The aim of this study is to improve the genetic diagnosis of NOA, by identifying new genes involved in human NOA and to better assess the chances of successful sperm extraction according to the individual's genotype. Exome sequencing was performed on 96 NOA-affected individuals negative for routine genetic tests. Bioinformatics analysis was limited to a panel of 151 genes selected as known causal or candidate genes for NOA. Only highly deleterious homozygous or hemizygous variants were retained as candidates. A likely causal defect was identified in 16 genes in a total of 22 individuals (23%). Six genes had not been described in man (DDX25, HENMT1, MCMDC2, MSH5, REC8, TDRKH) and 10 were previously reported (C14orf39, DMC1, FANCM, GCNA, HFM1, MCM8, MEIOB, PDHA2, TDRD9, TERB1). Seven individuals had defects in genes from piwi or DNA repair pathways, three in genes involved in post-meiotic maturation, and 12 in meiotic processes. Interestingly, all individuals with defects in meiotic genes had an unsuccessful sperm retrieval, indicating that genetic diagnosis prior to TESE could help identify individuals with low or null chances of successful sperm retrieval and thus avoid unsuccessful surgeries.

Keywords: genetic diagnosis; genetics of male infertility; non-obstructive azoospermia; whole-exome sequencing.

Figure 1

STRING analysis of physical and functional protein-protein interactions between the proteins encoded by the 151 candidate genes including in the NOA panel Analysis performed using STRING: https://string-db.org/. Two main clusters are highlighted in blue circles, loosely regrouping meiotic genes (left) and PIWI and DNA repair genes (right).

Figure 2

Definition and schematic representation of the different NOA sub-phenotypes illustrated by subjects’ histological sections (A) The testicular biopsies were categorized into different histopathological patterns, indication of the total number of individuals with each anomaly. Normal spermatogenesis: the seminiferous tubules are lined by a thin basement membrane and the germinal epithelium shows normal progression from spermatogonia to spermatozoa along with spermatocytes and spermatids. Hypospermatogenesis (HS): the germinal epithelium shows all the stages of germ cells but their number is reduced. Sertoli cell only syndrome: the tubules contain only Sertoli cells and no germ cells. Testicular degeneration: including both seminiferous tubule hyalinization and degenerating tubules. Hyalinized tubules are characterized by a thickened basement membrane, smaller diameter devoid of epithelial cells, and collagen deposition. Degenerating tubules are characterized by hypocellularity. Germ cell maturation arrest (pre-meiotic arrest [PreMA], meiotic arrest [MA], and post-meiotic arrest [Post-M]): at a specific cell stage the process of spermatogenesis is arrested. Mixed pattern (not shown): there is variation in the histopathological pattern in the same testicular biopsy. (B) Proportion of individuals with successful TESE according to the testis histology. (C) Examples of testis sections from individuals with different testicular defects.