[Clinical and genetic characteristics of 62 children with mitochondrial epilepsy]

Objective: To summarize the clinical and genetic characteristics of children with mitochondrial epilepsy. Methods: Clinical data of 62 children who were clinically and genetically diagnosed with mitochondrial epilepsy by the Department of Neurology, Beijing Children's Hospital from October 2011 to December 2018 were analyzed retrospectively, and the control of epilepsy was followed up. T test or χ(2) test were used to analyze the related factors affecting the prognosis of epilepsy between the effective group and the ineffective group. Results: Of the 62 patients, 33 were male and 29 were female. The age of onset was 3.38 (0-12.00) years; for the type of seizures, 68% (42/62) of the patients had focal seizures, generalized or secondary generalized tonic-clonic seizures were seen in 32% (20/62), myoclonic seizures in 23% (14/62), spastic seizures in 7 cases, tonic seizures in 4 cases, absence seizure, atonic seizure and clonic seizure in 1 case each; 16 cases (26%) had status epilepticus, of whom 6 cases had epilepsia partialis continua; 52% (32/62) had 2 or more types of seizures. The clinical phenotypes were mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) in 29 cases, Leigh syndrome (LS) in 11 cases, combined oxidative phosphorylation deficiency in 6 cases, myoclonus epilepsy with ragged-red fibers in 5 cases, Alpers syndrome in 4 cases, pontocerebellar hypoplasia type 6 and mitochondrial DNA depletion syndrome 9 in 2 cases each, mitochondrial complex Ⅰ deficiency nuclear type 20, progressive cavitating leukoencephalopathy, and biotinidase deficiency in 1 case each. Of the 62 cases, 40 cases (65%) had mitochondrial DNA (mtDNA) variations, of which 26 cases had m.3243A>G variants, 6 cases had m.8344A>G variants, and 3 cases had m.8993T>G/C variants, m.3271T>C, m.3481G>A, m.3946G>A, m.13094T>C, m.14487T>C variant was in 1 case each; nuclear DNA (nDNA) variations were identified in 22 cases (35%), of which 7 cases carrying variations in mitochondrial ammonia acyl tRNA synthetase coding gene, mutations in POLG and the gene encoding complex Ⅰ were in 4 cases each, variations in SUCLG1 and SDHA genes were in 2 cases each, and variations in PDHA1, BTD and TRIT1 genes were in 1 case each. Forty-three patients were followed up, and the follow-up time was 20 (3-84) months. According to the follow-up results, the anti-epilepsy treatment was effective in 19 cases (44%) and ineffective in other 24 cases (56%). The onset age of the effective group was 3.42 (0-11.50) years and that of the ineffective group was 0.92 (0-9.50) years. The onset duration of the effective group was 0 (0-7.00) years and that of the ineffective group was 0 (0-4.83) years. There was no significant difference between the effective group and the ineffective group (t=1.662, 0.860; P=0.104, 0.395). In the effective group and the ineffective group, 12 cases and 9 cases used less than 2 kinds of antiepileptic drugs, 7 cases and 15 cases used more than or equal to 2 kinds of antiepileptic drugs, 13 and 15 cases had first epilepsy, 6 and 9 cases had non-first epilepsy, 14 and 11 cases had mtDNA variation, 5 and 13 cases had nDNA variation, respectively. There was no significant difference between the two groups (χ(2)=2.794, 0.164, 3.380; P=0.095, 0.686, 0.066). Conclusions: The types of seizures with mitochondrial epilepsy in children varied, with focal motor seizures being the most common, followed by generalized or secondary generalized tonic-clonic seizures. Most children have more than two types of seizures. MELAS is the most common clinical phenotype, followed by LS; mtDNA variation is the dominant gene variation, of which m.3243A>G variation is the most common hotspot variation, followed by gene variation encoding mitochondrial aminoacyl tRNA synthase.