['MUTYH-associated polyposis syndrome is inherited as a recessive trait and is characterized by the presence of colorectal adenomas and cancer predisposition. Carriers of biallelic mutations in the base excision repair gene MUTYH are exposed to an increased risk of colorectal cancer. The aim of this study was to investigate the pathogenicity of the 13-base-pair deletion, c.504 + 19_504 + 31del13, located on intron 6 of the MUTYH gene, which was identified in 2 unrelated Greek patients with MUTYH-associated polyposis.', 'Genomic DNA and total RNA were extracted from peripheral blood lymphocytes of 2 unrelated families with polyposis. Screening of the entire coding region of the APC gene and MUTYH gene was performed by direct sequencing.', 'cDNA analysis of a patient homozygous for the c.504 + 19_504 + 31del13 mutation, and a patient heterozygous for the c.504 + 19_504 + 31del13/c.1437_1439delGGA mutations, revealed complete skipping of MUTYH exon 6. A part of the glycosylase catalytic domain, the pseudo-helix-hairpin-helix motif, is located within exon 6, which enhances the pathogenic effect of the mutation.'] Is an in-frame exon-skipping MUTYH mutation associated with early-onset colorectal cancer?