ARID1A, a bona fide tumor suppressor, is the third most mutated gene in human colorectal cancer. However, so far no study has investigated this gene in Iranian patients. In this paper we report a novel mutation in the ARID1A gene in colon carcinoma from an Iranian patient. As far as we know, it also is the first report on the mutation of ARID1A gene in an Iranian patient. Furthermore, the impact of this mutation on ARID1A expression changes was examined by immunohistochemistry.

Twenty primary colorectal carcinomas were examined for identification of possible mutations of ARID1A. To do so, the exon 3 of the ARID1A gene were amplified by the PCR and analyzed by Sanger sequencing. The expression level of ARID1A protein in cancerous tissue sample, harboring ARID1A mutation and matched adjacent nontumorous tissue sample was detected by immunohistochemistry.

Sanger sequencing revealed a novel heterozygous nonsense mutation of cytosin at nucleotide 1653 to guanine in ARID1A gene resulting in premature termination of the 2285 amino acid protein at the 551st codon. This novel mutation was predicted to be pathogenic by Mutation Taster. Immunohistochemical analysis revealed loss of ARID1A protein expression in colon cancer tissue.

Given that loss of ARID1A expression plays an important role in the development and progression of various cancers including colorectal cancer, it is likely that our novel mutation possesses high oncogenic activity. This mutation expands the spectrum of ARID1A gene pathogenic mutations among colorectal cancer patients.