Micro-exons of the cardiac myosin binding protein C gene: flanking introns contain a disproportionately large number of hypertrophic cardiomyopathy mutations.

Hypertrophic cardiomyopathy is primarily caused by mutations in genes encoding cardiac sarcomere proteins. Large screening studies identify mutations in 35-65% of the diagnosed patients and 15-30% of these are discovered within the MYBPC3 gene encoding the cardiac myosin binding protein C. The aim of this study is to determine whether intronic variation flanking the three micro-exons in MYBPC3 is disease-causing. Two hundred and fifty unrelated patients with hypertrophic cardiomyopathy were genotyped in MYBPC3, using automated single-strand conformation polymorphism, and sequenced for confirmation. Mutations located in the flanking introns of the MYBPC3 micro-exons were examined using in silico methods. Ectopic expression of mRNA in blood leukocytes in the respective patients was examined using reverse transcription-PCR. A total of seven mutations were discovered in the introns flanking the two micro-exons 10 and 14, but none were found in introns flanking exon 11. Functional studies together with co-segregation analysis indicate that four mutations are associated with HCM, in the respective patients. All four mutations result in premature termination codons, which suggests that haploinsufficiency is a pathogenic mechanism of this type of mutation. It is demonstrated that the use of in silico methods together with RNA studies on peripheral blood leukocytes is a useful tool to evaluate the potential effects of mutations on pre-mRNA splicing.