Deletions in the Azoospermia Factor C (AZFc, OMIM #415000) region of the long arm of the Y chromosome proximal to the large heterochromatic block, including polymorphisms and deletions in the Ubiquitin-specific peptidase 9 and Y-linked (USP9Y, OMIM #400005) gene [16], have been identified as the most common cause of male factor infertility, particularly spermatogenic failure [17]. The gene discussed is USP9Y; the disease is spermatogenic failure.