Microrna Copy Number Abnormalitie Kelainan Nomor Salin Microrna Di Kanker Kolorektal Keluarga

Abstract

Background The majority of the familial colorectal cancer (CRC) cases cannot be explained by known gene defects, suggesting the existence of other genetic risk factors. In an approach to identify such risk factors, we recently performed a screen for copy number variations (CNVs) in highrisk CRC patients and found, among other lesions, several small deletions affecting microRNA genes. MicroRNAs are negative regulators of approximately 30% of the genes in the human genome, including numerous tumor suppressor genes and oncogenes. Methods In order to comprehensively investigate copy number variation in microRNA genes, and to reveal whether such variations may affect CRC predisposition, we screened for CNVs affecting microRNA genes in 17 unexplained familiar early-onset CRC patients using a custom made ultimate (tiling) resolution oligo array containing 695 miR genes. We performed MLPA, q-PCR and PCR to validate all CNVs candidate. Results We found various small (0.2 - 23 kb) constitutional deletions and duplications affecting single microRNA genes. Several of these CNVs, validated using PCR-based technique, were only detected in patients and not in controls. For example miR-646 was found to be duplicated in patient but in 250 controls no duplication was found. MiR-770 was deleted in another patient, whereas no CNVs at this position were found in 94 controls. Conclusion We conclude that CNVs of smaller size (<1 Mb) affecting miRNA genes do occur and can be identified using custom oligo array. Nevertheless, further optimization needs to be done to reduce the noise and false positive results generated which complicate the validation process. On the other hand using an in-house database, some of the miRs are indeed affected by polymorphic CNVs and many others are still unknown. Overall we showed CNVs in microRNA genes are more common than previously thought, and some of them may be associated with CRC predisposition. Keywords: Familial colorectal cancer, copy number variations, microRNA, microarray