TXNDC8 (thioredoxin domain containing 8), also known as SPTRX3, is a germ line-specific thioredoxin localized to the Golgi apparatus of spermatocytes and spermatids 1. Its primary function involves reducing disulfide bonds and facilitating post-translational modifications of proteins required for acrosomal biogenesis 1. TXNDC8 is uniquely expressed during male germ cell development and becomes abnormally retained in the nuclear vacuoles and superfluous cytoplasm of defective spermatozoa 2. While related thioredoxins (Txndc2 and Txndc3) are critical for protecting mature spermatozoa against oxidative stress and age-related DNA damage 3, TXNDC8 serves as a biomarker of spermatogenic dysfunction. High semen levels of TXNDC8 (>15% positive spermatozoa) correlate with reduced pregnancy rates in assisted reproductive therapy, with affected couples experiencing nearly two-thirds reduction in conception likelihood compared to those with low TXNDC8 levels 4. TXNDC8 content also correlates positively with sperm DNA fragmentation and negatively with sperm concentration and motility 5. Notably, fathers of multiple births show significantly lower TXNDC8 levels than those conceiving singletons 5, suggesting TXNDC8 as a predictive marker for ART outcomes and pregnancy complications.