A novel mitochondrial DNA point mutation associated with mitochondrial encephalocardiomyopathy.

A novel mitochondrial DNA (mtDNA) mutation at position nt 4320 in the tRNA(Ile) gene was associated with severe encephalopathy in a 7-month-old infant, who died of intractable hypertrophic cardiomyopathy. The mutation was present in heteroplasmic fashion (88%) in muscle and fulfills accepted criteria for pathogenicity. This is the fourth pathogenic mutation identified in this gene, which appears to be a "hotspot" for deleterious mutations affecting the heart. This report adds to the evidence of genetic heterogeneity in hypertrophic cardiomyopathies.