Two compound frame-shift mutations in succinate dehydrogenase gene of a Chinese boy with encephalopathy

Objective: To investigate respiratory chain complex II deficiency resulted from mutation in succinate dehydrogenase gene (SDH) encoding complex II subunits in China. Methods: An 11-year-old boy was admitted to our hospital. He had a history of progressive psychomotor regression and weakness since the age of 4 years. His cranial magnetic resonance imaging revealed focal, bilaterally symmetrical lesions in the basal ganglia and thalamus, indicating mitochondrial encephalopathy. The activities of mitochondrial respiratory chain enzymes I−V in peripheral leukocytes were determined via spectrophotometry. Mitochondrial DNA and the succinate dehydrogenase A (SDHA) gene were analyzed by direct sequencing. Results: Complex II activity in the leukocytes had decreased to 33.07 nmol/min/mg mitochondrial protein (normal control 71.8 ± 12.9); the activities of complexes I, III, IV and V were normal. The entire sequence of the mitochondrial DNA was normal. The SDHA gene showed two heterozygous frame-shift mutations: c.G117G/del in exon 2 and c.T220T/insT in exon 3, which resulted in stop codons at residues 56 and 81, respectively. Conclusions: We have described the first Chinese case of mitochondrial respiratory chain complex II deficiency, which was diagnosed using enzyme assays and gene analysis. Two novel, compound, frame-shift mutations, c.G117G/del in exon 2 and c.T220T/insT in exon 3 of the SDHA gene, were found in our patient.