The CA XII gene encodes Carbonic Anhydrase 12, a zinc metalloenzyme responsible for catalyzing the reversible hydration of carbon dioxide. The CA XII protein localizes in the basolateral membrane of ductal epithelia in the sweat gland and in the apical membrane in airway epithelia. By carrying out its function, the CA XII protein is believed to play a role in maintaining cellular pH and controlling salt transport. 

Mutations in the gene have been linked to Isolated Hyperchlorhidrosis, a condition characterized by excessive sweat chloride levels, hyponatremic dehydration, hyperkalemia and a failure to thrive. A recent study has further suggested that along with the sweat glands, CA XII may also play a role in the function of the pulmonary airways. 

The CA12 gene is located on the long arm of chromosome 15. It spans a length of 60.7 kb of DNA and its coding sequence is spread across 11 exons. It encodes a 39.4 kDa protein product consisting of 354 amino acids. An additional isoform of the CA12 protein, consisting of 343 amino acids, is encoded by an alternatively spliced transcript variant. The gene is found to be overexpressed in the colon, kidney, prostate, intestine and activated lymphocytes. The p.Glu143Lys substitution in the CA12 gene has been identified in several Bedouin families affected by Hyperchlorhidrosis.