The observed infertility in Brn-3b knockout mice, coupled with single-cell RNA sequencing (scRNA-seq) data revealing significantly reduced populations of POU4F2 (Brn-3b)-expressing cells in infertile men with azoospermia and Klinefelter syndrome, highlights its importance in human spermatogenesis. This evidence concerns the gene POU4F2 and Azoospermia.