Endocrine Abstracts

Purpose: Non-Obstructive Azoospermia (NOA), occurring in approximately 1% of men, has an unknown etiology in the majority of cases. This study aims at evaluating the diagnostic efficiency of a gene panel contemplating all known genes associated with azoospermia in mice.

Subjects and methods: Design of a ‘mouse azoospermia’ gene panel through the consultation of MGI; selection of 175 mouse azoospermia genes with human orthologues; selection of 31 idiopathic NOA patients from a total of 1300 infertile patients and selection of a familial case (2 brothers) of NOA. Next-Generation Sequencing in the 33 selected NOA men. Characterization of the discovered gene defects in human testis tissue: i) meiotic studies in carriers of RNF212 and STAG3 mutations; ii) RNF212 and STAG3 expression profile through qPCR.

Results: Homozygous pathogenic RNF212 variant was identified in two brothers (consanguineous parents) and biallelic variants in STAG3 in a sporadic patient. Meiotic studies in the siblings revealed normal meiotic entry/XY body formation but an increase of apoptotic metaphases while in the STAG3 mutation carrier normal meiotic entry but no XY body formation.

Conclusion: By using a hypothesis-driven approach which consisted in the sequencing of 175 genes, for the first time, we report biallelic variants in STAG3 in one sporadic patient, and a homozygous RNF212 variant in the two brothers as the genetic cause of NOA. Meiotic studies allowed the detection of the functional consequences of the mutations and provided information on the role of STAG3 and RNF212 in human male meiosis. Our approach was relatively successful since we could diagnose a candidate gene mutation in 9% of idiopathic NOA cases (2/33). This proportion increases up to 40–50% if we consider only patients affected by meiotic arrest. Our study represents an additional step towards elucidating the genetic basis of early spermatogenic failure. We propose the inclusion of RNF212 and STAG3 in a future male infertility diagnostic gene panel. More than half of the 175 sequenced genes are reported to affect also female reproduction in mice (among them Rnf212 and Stag3) and STAG3 mutations were first described as a cause of female infertility (POI) and ovarian cancer. Hence, our results stimulate further research on shared genetic factors causing both POI and NOA. The diagnosis of such genetic factors implies that genetic counselling for NOA has relevance not only to the male family members and male descendants but also to female relatives.