PURPOSE Somatic mutations occur at early stages of adenoma and accumulate throughout colorectal cancer (CRC) progression. The aim of this study was to characterize the mutational landscape of stage II tumors and to search for novel recurrent mutations likely implicated in CRC tumorigenesis. DESIGN The exomic DNA of 42 stage II, microsatellite stable, colon tumors and their paired mucosae were sequenced. Other molecular data available in the discovery dataset (gene expression, methylation, and CNV) was used to further characterize these tumors. Additional datasets comprising 553 CRC samples were used to validate the discovered mutations. RESULTS As a result, 4,886 somatic single nucleotide variants (SNVs) were found. Almost all SNVs were private changes, with few mutations shared by more than one tumor, thus revealing tumor-specific mutational landscapes. Nevertheless, these diverse mutations converged into common cellular pathways such as cell cycle or apoptosis. Among this mutational heterogeneity, variants resulting in early stop-codons in the AMER1 (also known as FAM123B or WTX) gene emerged as recurrent mutations in CRC. Loses of AMER1 by other mechanisms apart from mutations such as methylation and copy number aberrations were also found. Tumors lacking this tumor suppressor gene exhibited a mesenchymal phenotype characterized by inhibition of the canonical Wnt pathway. CONCLUSION In silico and experimental validation in independent datasets confirmed the existence of functional mutations in AMER1 in approximately 10% of analyzed CRC tumors. Moreover, these tumors exhibited a characteristic phenotype.

DMD nonsense and frameshift mutations lead to severe Duchenne muscular dystrophy while in-frame mutations lead to milder Becker muscular dystrophy. Exceptions are found in 10% of cases and the production of alternatively spliced transcripts is considered a key modifier of disease severity. Several exonic mutations have been shown to induce exon-skipping, while splice site mutations result in exon-skipping or activation of cryptic splice sites. However, factors determining the splicing pathway are still unclear. Point mutations provide valuable information regarding the regulation of pre-mRNA splicing and elements defining exon identity in the DMD gene. Here we provide a comprehensive analysis of 98 point mutations related to clinical phenotype and their effect on muscle mRNA and dystrophin expression. Aberrant splicing was found in 27 mutations due to alteration of splice sites or splicing regulatory elements. Bioinformatics analysis was performed to test the ability of the available algorithms to predict consequences on mRNA and to investigate the major factors that determine the splicing pathway in mutations affecting splicing signals. Our findings suggest that the splicing pathway is highly dependent on the interplay between splice site strength and density of regulatory elements.

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