TDRD5 (Tudor Domain Containing 5) is essential for male germline integrity, functioning as a critical component of the piRNA (PIWI-interacting RNA) pathway. 1 TDRD5 interacts with MIWI (PIWIL1) through Tudor domain binding to mediate piRNA amplification and transposon silencing, processes necessary for controlling retrotransposons during spermatogenesis. 2 The protein localizes to cytoplasmic granules including chr1 bodies and P granules, which are essential subcellular structures for piRNA biogenesis and post-meiotic gene regulation. 1 Mechanistically, TDRD5 participates in piRNA-mediated DNA methylation and subsequent repression of transposable elements. 3 It acts as a cofactor in piRNA-mediated transcript silencing and helicase effector function. Loss or dysfunction of TDRD5 impairs pachytene piRNA biogenesis and destabilizes chr1 body assembly. Clinically, deleterious TDRD5 variants cause severe male infertility. Homozygous missense (p.A1015T) and nonsense (p.E765*) mutations result in severe oligoasthenoteratozoospermia, with affected spermatozoa displaying multiple heads/flagella and acrosomal hypoplasia. 2 Reduced TDRD5 expression correlates with non-obstructive azoospermia subtypes including maturation arrest and Sertoli cell-only syndrome. 4 TDRD5 variants represent novel candidate genes for male infertility pathogenesis, with intracytoplasmic sperm injection showing therapeutic potential for affected patients.