Catalyzes the decarboxylation of L-aspartate, 3-sulfino-L- alanine (cysteine sulfinic acid), and L-cysteate to beta-alanine, hypotaurine and taurine, respectively. The preferred substrate is 3- sulfino-L-alanine. Does not exhibit any decarboxylation activity toward glutamate. . This is the function of ENSG00000139631 (CSAD, cysteine sulfinic acid decarboxylase).