Mitochondrial respiratory chain enzyme assay and DNA analysis in peripheral blood leukocytes for the etiological study of Chinese children with Leigh syndrome due to complex I deficiency.

Mitochondrial respiratory chain complex I enzyme deficiency is the most commonly seen mitochondrial respiratory chain disorder. Although screening and diagnostic methods are available overseas, clinically feasible diagnostic methods have not yet been established in China. In this study, four Chinese boys with Leigh syndrome due to complex I deficiency were diagnosed by mitochondrial respiratory chain enzyme assay and DNA analysis using peripheral blood leukocytes. Four patients were admitted at the age of 5-14 years because of unexplained progressive neuromuscular symptoms, including motor developmental delay or regression, weakness, and seizures. Their cranial magnetic resonance imaging revealed typical finding as Leigh syndrome. Peripheral leukocyte mitochondrial respiratory chain complex I activities were found decreased to 9.6-33.1 nmol/min/mg mitochondrial protein(control 44.0 ± 5.4 nmol/min/mg). The ratios of complex I to citrate synthase activity were also decreased (8.9-19.8% in patients vs. control 48 ± 11%). Three mtDNA mutations were identified from three out of four patients, supporting the diagnosis of complex I deficiency. Point mutations m.10191T>C in mitochondrial ND3 gene, m.13513G>A in ND5 gene and m.14,453G>A in ND6 gene were detected in three patients.