Carbonic anhydrases are a large family of zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide. Carbonic anhydrases are involved in various biological processes, including respiration, calcification, acid-base balance, bone resorption, as well as the formation of aqueous humor, cerebrospinal fluid, saliva, and gastric acid.Carbonic anhydrase 12 (CA12) is a type I membrane protein that is highly expressed in normal tissues such as the kidney, colon, and pancreas, and is overexpressed in 10% of renal clear cell carcinomas. Two transcript variants encoding different isoforms of CA12 have been identified. Researchers suggest that genetic mutations in CA12 may be associated with autosomal recessive inherited hyponatremia, as sweating leads to salt depletion.