FHDC1 and Azoospermia: Notably, when comparing Brn-3b mRNA expression patterns, we observed significantly higher expression levels in testis biopsies from normozoospermic controls compared to samples from infertile men, including individuals with non-obstructive azoospermia (INF1), a case of retrograde ejaculation (INF2), and patients with Klinefelter syndrome (KS).