SLC22A14 is a mitochondrial riboflavin transporter localized to the inner membrane of the spermatozoa midpiece, essential for male fertility 1. The transporter mediates riboflavin uptake, which serves as a precursor for FAD and FMN cofactors critical for oxidative phosphorylation and energy metabolism in sperm 1. SLC22A14-dependent riboflavin transport is required for fatty acid β-oxidation and tricarboxylic acid cycle function, processes vital for spermatozoa motility and ATP generation 1. Loss of functional SLC22A14 causes disrupted flavoenzyme activity, impaired oxidative phosphorylation, and male infertility in mice 1. Clinically, reduced SLC22A14 expression correlates with idiopathic asthenozoospermia (reduced sperm motility) in infertile men 2. Genetic variants in SLC22A14 have been associated with paclitaxel toxicity in lung cancer patients 3 and sorafenib response in hepatocellular carcinoma 4, suggesting pharmacological roles beyond reproduction. The gene was recently deorphaned, transitioning from an uncharacterized transporter to a functionally defined protein with clear physiological importance in sperm bioenergetics 5.