IRGC (immunity-related GTPase cinema) is a testis-specific protein required for male fertility through regulation of sperm motility 1. Unlike other immunity-related GTPases that function in pathogen defense, IRGC has evolved a specialized reproductive role 2. Mechanistically, IRGC mediates physical interaction between lipid droplets and mitochondria in mature spermatozoa, facilitating lipid metabolism-dependent energy production necessary for flagellar movement 1. This function is critical for fibrous sheath formation and positive regulation of flagellated sperm motility, as indicated by its localization to the sperm flagellum and mitochondrial sheath 1. Clinically, IRGC expression is significantly reduced in asthenozoospermia (reduced sperm motility) patients compared to healthy individuals, establishing it as a potential biomarker for male infertility 1. The discovery of IRGC's lipid-mitochondrial regulatory axis suggests that therapeutic interventions targeting lipid metabolism could address asthenozoospermia-related fertility problems. This represents a unique application of the IRG protein family, which has been dramatically reduced in humans to two functional members (IRGC and IRGM), with IRGC specializing in reproduction rather than immunity 2.