Sialate O-acetylesterase belongs to the family of hydrolases, specifically those acting on carboxylic ester bonds. It is widely expressed with high expression in the testis, prostate, and colon. The systematic name of this enzyme class is N-acyl-O-acetylneuraminate O-acetylhydrolase. Other names in common use include N-acetylneuraminate acetyltransferase, sialate 9(4)-O-acetylesterase, and sialidase. Sialate O-acetylesterase catalyzes the removal of O-acetyl ester groups from position 9 of the parent sialic acid, N-acetylneuraminic acid. Defects in Sialate O-acetylesterase are a cause of autoimmune disease type 6 (AIS6). Individuals manifesting susceptibility to autoimmune disease type 6 can suffer from juvenile idiopathic arthritis, rheumatoid arthritis, multiple sclerosis, Sjogren syndrome, systemic lupus erythematosus, type 1 diabetes, ulcerative colitis, and Crohn disease.