Purpose: To determine the molecular basis of familial, autosomal-recessive, non-obstructive azoospermia in a consanguineous Iranian Jewish family.
Methods: We investigated the genetic cause of non-obstructive azoospermia in two affected siblings from a consanguineous family. Homozygosity mapping in the DNA samples of the patients and their normospermic brother was followed by exome analysis of one of the patients. Other family members were genotyped for the mutation by Sanger sequencing. The mutation effect was demonstrated by immunostaining of the patients' testicular tissue.
Results: The two patients were homozygous for a splice site mutation in SYCE1 which resulted in retention of intron three in the cDNA and premature stop codon. SYCE1 encodes a Synaptonemal Complex protein which plays an essential role during meiosis. Immunostaining of patient's testicular tissue with anti-Syce1 antibody revealed an undetectable level of Syce1. Histological examination of the patients' tissue disclosed immature-stages spermatocytes without mature forms, indicating maturation arrest.
Conclusion: The significance of most synaptonemal complex proteins was previously demonstrated in a mutant mouse model. The present report underscores the importance of synaptonemal complex proteins in spermatogenenesis in humans. Our new approach, combining homozygosity mapping and exome sequencing, resulted in one of the first reports of an autosomal-recessive form of NOA.