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Novel APC Promoter and Exon 1B Deletion and Allelic Silencing in Three Mutation-Negative Classic Familial Adenomatous Polyposis Families

The ~80% of individuals with classic familial adenomatous polyposis (FAP) have detectable mutations in the coding sequence of the adenomatous polyposis coli (APC) gene. To investigate the 20% of families without detectable causative mutations, we used exome sequencing and second-generation sequencing of the APC locus including non-coding regions. We identified a novel ~11kb deletion 44kb upstream of APC that was present only in affected individuals of three kindreds. SNP analysis showed that this ~11kb deletion was accompanied by silencing of one of the APC alleles in blood-derived RNA of affected individuals.