- An mtDNA mutation in the initiation codon of the cytochrome C oxidase subunit II gene results in lower levels of the protein and a mitochondrial encephalomyopathy. Clark, K.M., Taylor, R.W., Johnson, M.A., Chinnery, P.F., Chrzanowska-Lightowlers, Z.M., Andrews, R.M., Nelson, I.P., Wood, N.W., Lamont, P.J., Hanna, M.G., Lightowlers, R.N., Turnbull, D.M. Am. J. Hum. Genet. (1999)