TENT5D (terminal nucleotidyltransferase 5D) is a noncanonical poly(A) polymerase that catalyzes adenosine transfer to mRNA poly(A) tails, functioning as a key regulator of mRNA stability 1. Structurally belonging to the nucleotidyltransferase fold superfamily 2, TENT5D localizes to endoplasmic reticulum membranes where it selectively stabilizes mRNAs encoding secretory and ER-imported proteins, thereby promoting expression of secretory cargoes and proteins involved in protein folding and trafficking 1. TENT5D is predominantly expressed in spermatid heads and flagella during gametogenesis 3. Pathogenic mutations in X-linked TENT5D cause male infertility through teratozoospermia and oligoasthenoteratozoospermia (OAT) 43. Loss-of-function variants result in severely decreased sperm count with multiple morphologic abnormalities including abnormal flagellar structures with disrupted 9+2 microtubular organization and poor motility 43. TENT5D deficiency impairs post-transcriptional gene expression regulation critical for proper spermatogenesis 5. Clinically, intracytoplasmic sperm injection (ICSI) successfully rescues male infertility caused by TENT5D mutations, achieving viable pregnancies 4. This represents an important therapeutic option for affected patients, as TENT5D mutations are rare but highly deleterious causes of unexplained male infertility.