The calpains, a family of calcium-dependent cysteine proteinases, and calpastatin, their endogenous inhibitor protein, are involved in the proteolysis of amyloid precursor protein, which is thought to be abnormal in patients with Alzheimer's disease (AD). Specific inhibitors of calpains attenuate amyloid beta peptide-induced neuronal death. We hypothesized that some AD patients have functionally deficient mutation(s) of the CAST gene encoding calpastatin, and we screened 40 Japanese patients with AD for mutations in the coding region of CAST. Nine polymorphisms, -82A/G, IVS7-96A/G, 669A/G, 1223C/G (Ser408Cys), IVS20-10C/T, IVS21-65G/A, IVS22+31T/C, IVS24+38Ins/DelA, and IVS25-32A/G, were identified. The 669A allele causes skipping of exon 11, leading to the loss of 13 residues. Comparisons between 101 patients and 90 controls revealed no significant association between CAST polymorphisms and risk for AD, indicating that genomic variations of CAST are not likely to be substantially involved in the etiology of AD.