ABSTRACT
Mitochondrial DNA-associated Leigh syndrome is a part of a continuum of progressive neurodegenerative disorders caused by abnormalities of mitochondrial energy generation. Mitochondrial T8993C and T8993G mutations account for 10-20% of these cases. T8993C is generally associated with milder phenotype than T8993G mutation. Here we report an Egyptian family with T8993C mutation with unusual early onset of severe phenotype in three sisters [consisting of regression of previously acquired motor and mental milestones after an attack of viral infection] and hypothyroidism as the only presenting symptom in their brother. The mother [like her son] carried the T8993C mutation and was asymptomatic. This unusual lack of manifestation could be attributed to different percentages of mutated mitochondrial DNA in the brain or muscle or perhaps to some unknown protective factor. The hypothyroidism could be a simple association, but to the best of our knowledge, no previous reports have described hypothyroidism in carriers of this mutation