Two novel mitochondrial tRNA mutations, A7495G (tRNA(Ser(UCN))) and C5577T (tRNA(Trp)), are associated with seizures and cardiac dysfunction.

We describe here two novel mitochondrial mutations associated with a complex mitochondrial encephalopathy. An A to G transition at position 7495 (MT-TS1 (MT-tRNSer(UCN))) was identified at 83% heteroplasmy in the muscle of a four year old female with ptosis, hypotonia, seizures, and dilated cardiomyopathy (Case 1). A homoplasmic C to T transition at position 5577 (MT-TW (MT-tRNATrp)) was found in a twenty-four year old woman with exercise intolerance, mild muscle weakness, hearing loss, seizures, and cognitive decline (Case 2). The phenotypic information provided here will assist in phenotype-genotype correlations should additional patients be reported in the future. The mutations can be added to the database of mitochondrial DNA variations in conserved regions which result in clinically diverse phenotypes with the shared markers of mitochondrial disease.