Comparison of biochemical and molecular diagnosis in children with leigh syndrome in Korea

Abstract

Leigh syndrome is known as the most representative mitochondrial disease involving abnormal energy production with progressive decline. Deficits of the respiratory chain is reported to be the major cause of Leigh syndrome, and mutations of the genes encoding subunits of the respiratory chain or assembly factors of respiratory chain complexes are said to be the underlying causes. The need for biochemical and molecular diagnosis to draw more accurate diagnosis or prognosis to support treatments is rapidly increasing. This study tried to compare the aspects of biochemical diagnosis and molecular diagnosis of mitochondrial respiratory chain complex defect in Leigh syndrome, using methods of biochemical enzyme assay and molecular genetic analysis respectively. We included total number of 82 patients who satisfied the clinical criteria of Leigh syndrome. All those patients went through muscle biopsy to perform biochemical enzyme assay to analyze mitochondrial respiratory chain complex enzyme and molecular diagnosis in order to find the underlying cause of Leigh syndrome. Genetic analysis was performed on all muscle tissues to search for the presence of specific, known mtDNA mutations for Leigh syndrome and SURF1 mutation. Clinical aspects of cases without mutation were compared with those of the cases with mutation. MRC defect was found in 47 (57.3%) out of 82 patients diagnosed upon clinical criteria. Most cases, 38 (46.3%) to be exact, had single MRC defect. MRC I defect was seen in 23 (28.0%) cases taking the first place and MRC IV defect in 15 (18.3%) following it. Among 82 patients subjected to the study with confirmed MRC defect in biochemical enzyme assay, mtDNA mutation was identified in 9 (11.0%) cases. T10191C mutation was seen in 3 (3.74%), G13513A and T8993C in 2 (2.4%) respectively. C11777A and G14459A were also seen in 1 case each. As for the deletion mutation, heterozygous 372delG (G124fsX126), a newly discovered novel mutation, was found in 3 patients. 844T>C (S282P) novel mutation, a point mutation, was found in 1 case and known 604G>C (A202H), 543C>T (F181F) polymorphism were observed in 19 and 23 patients each. Respective cases of splicing site mutation, IVS1+1 G>T, IVS8-1 G>A was also found. There were 35 patients without mutation and 12 with mutation including 9 with confirmed mtDNA mutation and 3 with SURF1 mutation. Continuous ventilator care and perinatal asphyxia were reported significantly more often in mutation(+) group, but otherwise there was no statistical difference in clinical symptoms between the two. In MRI, the percentage of multiple lesion, brain stem and thalamus lesion were significantly higher in mutation(+) group. As for MRC defect, statistically higher proportion of mutation(+) patients showed to have combined defect. Though there were only 3 cases with SURF1 gene mutation, they were distinctive cases severe enough to require continuous ventilator care and tube feeding. Further gene analysis on more extended group of patients will enable us not only to improve diagnostic precision but to understand mitochondrial disease one step more as well by revealing the correlation between its phenotypes and genotypes.