FAM9A (also designated TEX39A) is an X-linked gene encoding a testis-specific protein with sequence homology to SYCP3, a synaptonemal complex component 1. The protein localizes to the nucleus and nucleolus 1. FAM9A is expressed exclusively in testis and plays a role in spermatid development and meiotic processes 1. In male infertility investigations, hemizygous loss-of-function variants in FAM9A were identified in azoospermic men; however, these variants were also detected in control men, suggesting FAM9A loss-of-function is unlikely to be a monogenic cause of male infertility 2. FAM9A shows sex-specific genetic associations with inguinal hernia susceptibility in men 3. The gene is located within a low-copy repeat region (Xp22.3) that may predispose to chrX rearrangements 1. In Klinefelter syndrome (47,XXY), FAM9A was identified as a differentially expressed transcript marking undifferentiated somatic cell populations in degenerating testes, suggesting involvement in disrupted testicular cell maturation 4. FAM9A exhibits aberrant DNA hypomethylation in uterine leiomyoma, though its functional significance in this context remains unclear 5.