Screening for mutations in the open reading frame and promoter of the beta-amyloid precursor protein gene in familial Alzheimer's disease: identification of a further family with APP717 Val-->Ile.

Following the identification of mutations in the beta-amyloid precursor protein (APP) gene in familial, early onset Alzheimer's disease (AD), we have developed a screening protocol using single strand conformation analysis (SSCA) to screen exon 17 for the known mutations within APP. In addition, we used this protocol to screen the other seventeen exons of APP and a three hundred and thirty base pair regulatory region of the promoter for new mutations in 9 families with early onset AD. Exons 16 and 17, which encode the deposited beta-amyloid peptide, were screened in a further 10 families. Our screening procedure identifies all the reported mutations within APP. While we have identified a further family with APP717 Val-->Ile, we did not find any previously undescribed mutations. Screening of other exons of APP in 2 families in which we have previously reported mutations at APP717, failed to reveal other sequence abnormalities supporting the hypothesis that the mutations at APP717 cause the disease in these families. These data suggest that mutations in APP are a rare cause of familial early onset AD (3/21 families tested) and that within APP most, possibly all, mutations which cause AD are in exon 17.