TAC1 and Alzheimer disease: By measuring the conversion of somatostatin 28 to somatostatin 1–14 and the degradation of substance P (both substrates of EP24.15), as poor, less specific surrogates for EP24.15 in the temporal cortex, it was implied that regulation of EP24.15 was significantly altered in AD (Waters and David, 1995; Waters and Davis, 1997).