APC germ-line allele-specific expression in familial adenomatous polyposis

Abstract

e22037 Background: About 13% of Familial Adenomatous Polyposis (FAP) families and 70% of Attenuated FAP families remain with unknown molecular pathogenic cause after APC and MYH mutational analyses. Also, mutations can affect specific allele expression (ASE) at the germline level. The aim of the study was to determine the presence of germline ASE in the APC gene in FAP and AFP with and without detectable APC or MYH mutations. Methods: Germline RNA from fresh frozen and/or cultured lymphocytes of 17 APC/MYH-negative Polyposis (7 FAP, 10 AFAP) families (21 individuals) and 35 APC-mutated Polyposis (30 FAP, 5 AFAP) families (60 individuals) was analyzed. Fourteen controls were also studied. ASE was investigated by single nucleotide primer extension (SNuPE) of rs2229992 APC coding SNP. Results: In controls ASE was 1.04± 0.3. We found that 17% (3 of 17) APC/MYH(-) FAP and AFAP families showed ASE (range=1.17–1.39) and ASE co-segregated with disease. ASE was more intense in short-cultured lymphocytes except for two cases and completely reversed by puromycin treatment. Eleven of 35 (31%) APC-FAP/AFAP harbored ASE (range=1.20–7.76), and the mutant allele was underexpressed in each case. ASE was restricted to splicing (4 families), nonsense (3 families) and frameshift (3 families) mutations outside of exon 15. Puromycin reversed ASE in all cases analyzed. Conclusions: APC ASE is present in a significant proportion (17%) of APC/MYH(-) FAP or AFAP. ASE, due to nonsense-mediated decay (NMD), is present in APC-FAP and is associated with specific mutation location, similar to reports for other hereditary syndromes. No significant financial relationships to disclose.