CCDC9 (coiled-coil domain containing 9) is a probable component of the exon junction complex (EJC), a multiprotein complex that associates upstream of exon-exon junctions on mRNAs and functions as a positional landmark for post-transcriptional processes including mRNA export, nonsense-mediated mRNA decay, and translation regulation. The protein contains coiled-coil domains and exhibits RNA and protein binding capabilities. CCDC9 has critical relevance in male reproductive function. Biallelic missense substitutions in CCDC9 have been identified as causative genetic variants in male infertility cases from consanguineous families 1. A homozygous pathogenic variant (p.Ser109Leu) causes severe asthenozoospermia through substantial reduction of CCDC9 protein levels and severe damage to spermatozoan morphology and ultrastructure, particularly affecting midpiece organization and mitochondrial sheath integrity 2. Beyond reproduction, circular RNA circCCDC9 shows disease-protective functions in other tissues. CircCCDC9 overexpression protects the blood-brain barrier and inhibits apoptosis in ischemic stroke models by suppressing Notch1 signaling 3. In gastric cancer, circCCDC9 functions as a tumor suppressor by acting as a competing endogenous RNA for miR-6792-3p, thereby relieving miR-6792-3p-mediated repression of CAV1 and inhibiting cancer cell proliferation, migration, and invasion 4. Clinically, CCDC9 represents an emerging biomarker for genetic male infertility diagnosis and a potential therapeutic target for ischemic stroke and gastric cancer management.