AIG1 (androgen induced 1) is a multipass transmembrane hydrolase that specifically degrades bioactive fatty acid esters of hydroxy fatty acids (FAHFAs) but not other major lipid classes 1. The enzyme functions as an atypical threonine hydrolase, requiring conserved threonine and histidine residues for catalytic activity and showing preference for FAHFAs with branching distal from the carboxylate head group 1. AIG1 was originally identified as an androgen-inducible gene in human dermal papilla cells, with expression stimulated by dihydrotestosterone and showing higher expression levels in males than females 2. The protein exists in two splice variants differing by 52 amino acids and contains multiple hydrophobic domains 2. Clinically, AIG1 plays a crucial role in metabolic regulation through the IRF3/AIG1 axis, where inflammation-induced AIG1 expression in adipocytes promotes insulin resistance by reducing FAHFA levels 3. Additionally, AIG1 has been implicated as a prognostic biomarker in hepatocellular carcinoma, with reduced expression associated with shorter survival times and lymph node metastasis 4. The gene also shows evolutionary conservation across vertebrates, suggesting fundamental biological importance 5.