Dear Editor,rnThe PIWI proteins (originally P-element-induced wimpy testis in Drosophila) are predominantly present in the germ-line in diverse organisms and are involved in the processing of a class of small RNAs known as piRNAs (see Refs.1,2 for review).The human PIWI protein family consists of four members:PIWIL1-4.Of these,PIWIL4 is known to have essential roles in the first phases ofspermatogenesis:its expression is restricted to gonocytes and it is required for transposon silencing.3 The lack of this gene in mice causes meiotic arrest in spermatogenesis.4 The goal of our study was to evaluate the frequency of several PIWIL4 genetic variants in our population to better define the relationship between PIWIL4 single nucleotide polymorphisms (SNPs) and both defective spermatogenesis and specific spermatogenic disorders.