Copy‐number analysis of Y‐linked loci in young men with non‐obstructive azoospermia: Implications for the rarity of early onset mosaic loss of chromosome Y

PURPOSE: Mosaic loss of chromosome Y (mLOY) is a common feature in elderly men. If mLOY can also occur in young men, it may lead to spermatogenic failure due to loss of spermatogenic genes. Indeed, previous studies detected the 45,X/46,XY karyotype in a few young men with spermatogenic failure. The present study aimed to clarify the frequency of cryptic mLOY in reproductive‐aged men with spermatogenic failure. METHODS: We studied 198 men at ages 24‐55 years who presented with etiology‐unknown non‐obstructive azoospermia. Prior this study, these patients underwent G‐banding analysis for 20 leukocytes and were found to have 46,XY karyotype. We analyzed copy numbers of chromosome Y in blood cells by using semi‐quantitative multiplex PCR for AMELY/AMELX, array‐based comparative genomic hybridization (CGH) for the AMELY locus, and droplet digital PCR for SRY, USP9Y, and UTY. RESULTS: Multiplex PCR showed borderline low AMELY/AMELX ratios in three patients. However, for the three patients, CGH excluded deletion of the AMELY locus, and droplet digital PCR suggested preserved copy numbers of all tested loci. CONCLUSION: This study highlights the rarity of leukocyte mLOY in reproductive‐aged men with spermatogenic failure. In addition, our data imply that standard karyotyping is sufficient to screen early onset mLOY.