PIWIL1 and Azoospermia: However, the contributions of individual PIWI genes to human spermatogenesis remain poorly defined.<h4>Case report</h4>Here, we report on a 29-year-old man with non-obstructive azoospermia and found to carry a homozygous frameshift mutation in PIWIL1 (NM_004764.5:c.1176_1179delAACT).