A Patient with MELAS Syndrome Carried an M.3243A>G Mutation in Mitochondrial DNA and Multiple Nuclear Genetic Variants: A Case Report

We discuss the involvement of nuclear genetic variants correlating to observed phenotype in this case study. In January 2020, the 19-year-old boy from Nantong, Jiangsu Province, China with epilepsy symptom was identified to have myelin loss in the motor and sensory nerves in the electromyogram examination. Brain magnetic resonance imaging (MRI) demonstrated high-intensity areas of small multifocal gray matter regions in the bilateral temporal, parietal, and occipital lobes. In the serum of the patient, the levels of lactate dehydrogenase (LDH) and lactic acid were higher than the normal range values in multiple tests. By subsequent whole exome sequencing (WES) including analysis of the mitochondrial genome, the patient was revealed to carry an m.3243A>G mutation in mitochondria MTTL1 gene which was confirmed by direct Sanger sequencing analysis. Thus, disease of the patient was diagnosed as mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome. According to WES analysis, the patient also carried multiple homozygous variants, which correlating to myelinloss and epilepsy in nuclear genes. The peripheral neuropathy of the patient carrying single mitochondrial m.3243A>G mutation could be caused by multiple nuclear DNA defect.