Whole exome investigation of infertility in men with azoospermia

Abstract

Male infertility is a disabling condition that affects 7% of men worldwide. The most severe form of male infertility is non-obstructive azoospermia (NOA) and approximately 20% of men with NOA have no identified cause. These patients are classified as idiopathic NOA. There is some data suggesting that the majority of men with idiopathic NOA have a genetic cause. The development of newer genetic sequencing technologies have allowed researchers to gain a better understanding of the genes contributing to spermatogenesis and those potentially causing NOA. In the present work, I have investigated clinical, biochemical, genetic and histological findings in men with NOA. I recruited 101 participants with azoospermia, and 48 of this cohort were diagnosed with idiopathic NOA. The cohort included 19 men with known causes of NOA and 24 men with obstructive azoospermia. Whole exome sequencing was performed on blood samples of men with idiopathic NOA for identification of candidate variants. I also recorded the available clinical factors, hormone profiles and testicular histopathology for all participants. The analysis of the sequenced data from the 48 men with idiopathic NOA identified 11 novel candidate variants. There were seven novel candidate Loss of Function (LoF) variants in men with NOA (MEIOB c.1140_1143del; FKBP6 c.469−2A>T; ANKRD36B c.2715T>G; FAM47C c.1536del; PKD2L2 c.1690C>T; FAM122C, c.427C>T; MCMDC2 c.108del) and four missense variants (YBX2 c.200G>A; MEIOB c.988A>C, PKD2L2 c.1391C>T; MCMDC2 c.119A>G). Two of the LoF (MEIOB and FKBP6) and two of the missense variants (MEIOB and YBX2) have functional evidence to support their association with azoospermia. The identified genes in NOA subjects showed a testicular phenotype matching the genes expression site during spermatogenesis. There was a significant decrease in testicular volume (p= 0.0392) and a significant increase in serum FSH (p=0.0014) in men with NOA compared to men with obstructive azoospermia (OA). Additionally, data is showing that identified variants have testicular histology phenotypes matching their site of expression. FKBP6, MEIOB, PKD2L2, and MCMDC2 genes are normally expressed in spermatocytes. Patients identified with variants in these genes were found to have histology phenotypes of maturation arrest at spermatocyte level. This could potentially be used to predict the histology phenotypes without surgical intervention. I have identified novel genetic variants in men with idiopathic NOA but further studies are needed to confirm causality. Genetic analysis can potentially improve our understanding of fertility by identifying genes involved in spermatogenesis and novel variants in men with infertility.