OXCT2 (3-oxoacid CoA-transferase 2) is a mitochondrial enzyme that catalyzes the transfer of CoA from succinate to acetoacetate, functioning as a key enzyme in ketone body catabolism 1. The enzyme operates through formation of an unstable anhydride intermediate between carboxylate groups of the enzyme and substrate. OXCT2 exists as testicular isoforms (Oxct2a and Oxct2b) that are specifically expressed in haploid spermatids, where they facilitate ketolysis in mitochondria 1. These testicular isoforms are single-copy intronless genes derived from transposition of the ancestral OXCT gene, with evidence of intrachromosomal gene conversion events 1. Clinically, OXCT2 has emerged as a potential biomarker in two distinct contexts. In reproductive medicine, OXCT2 is upregulated in advanced-age spermatozoa (40-51 years), where it associates with age-related proteomic changes that contribute to declining male fertility and impaired spermatogenesis 2. In dermatology, OXCT2 was identified as a hub gene in alopecia areata pathogenesis through weighted gene co-expression network analysis and machine learning approaches, suggesting involvement in autoimmune hair follicle targeting 3. These findings indicate OXCT2's role extends beyond canonical ketone metabolism to include reproductive aging and immune-mediated disease processes.