Heterogeneous nuclear ribonucleoprotein G-T (HNRNP G-T) mutations in men with impaired spermatogenesis.

The genetic cause of male subfertility due to impaired spermatogenesis is unknown in the majority of cases, but the general assumption is that it is a complex disorder. The aim of this study was to determine whether mutations occur in the HNRNP G-T gene in men with idiopathic impaired spermatogenesis. The heterogeneous nuclear ribonucleoprotein G-T (HNRNP G-T) gene is located in chromosomal region 11p15 that has been shown to be associated with impaired spermatogenesis. It is a member of the hnRNP gene family and is predominantly expressed in pachytene spermatocytes and round spermatids, where it is thought to affect splicing and signal transduction. We identified eight single nucleotide variants in our patient group of 153 subfertile men by sequencing the HNRNP G-T gene. Two of the mutations, R100H and G388del, did not occur in a control group of 143 normozoospermic men. The R100H mutation causes loss of a conserved arginine, thereby affecting a putative site of methylation possibly required for RNA-binding. Interestingly, this mutation was inherited from the mother. The G388del mutation causes loss of one non-conserved glycine located in a glycine stretch at the end of the protein that is not a known functional motif or domain. Our data show that HNRNP G -T mutations are not a frequent cause of impaired spermatogenesis. Nevertheless, the R100H mutation detected suggests that in some men mutations in the HNRNP G-T gene can cause impaired spermatogenesis.