ClinVar

In a patient with exercise intolerance, mild bilateral ptosis, limb weakness, and respiratory chain complex III deficiency, Pulkes et al. (2000) identified a novel heteroplasmic 5874A-G mutation in the mitochondrial tRNA tyrosine gene. Previous mutations associated with this clinical phenotype (excluding the ptosis) have been found in the mitochondrial cytochrome b gene (516020). The authors found that the tyrosine content is highest in the cytochrome b and COX III subunits, which may explain the clinical phenotype resulting from a defect in the tRNA-tyr gene. The mutation was found only in the patient's muscle and not in her blood or that of her relatives, suggesting somatic mutation.