Phenotypic differences between T-->C and T-->G mutations at nt 8993 of mitochondrial DNA in Leigh syndrome.

This study reports on a patient with Leigh syndrome with a T-to-C mutation at nucleotide 8993 of mitochondrial deoxyribonucleic acid (T8993C). The authors reviewed 10 Leigh syndrome patients, including ours, with T8993C. Compared with 18 reported patients with Leigh syndrome caused by a T-to-G mutation at nucleotide 8993 (T8993G), Leigh syndrome with T8993C was characterized by a significantly higher frequency of ataxia (P < 0.01). None of the reviewed T8993C-associated Leigh syndrome patients had retinitis pigmentosa, which is one of the characteristic findings in Leigh syndrome with T8993G. The milder symptoms of T8993C-Leigh syndrome can be explained by the milder complex V dysfunction; however, the higher frequency of ataxia in T8993C-Leigh syndrome requires more study.