线粒体脑肌病伴乳酸血症和卒中样发作综合征的临床特征及遗传学研究

目的探讨线粒体脑肌病伴乳酸血症和卒中样发作（MELAS）综合征临床与分子遗传学特征，寻找MELAS线粒体DNA（mtDNA）A3243G点突变比例与临床特征的关联性。方法对2001年1月至2008年1月在首都医科大学附属北京儿童医院神经内科住院和门诊临床疑似线粒体脑肌病的患儿，行外周血白细胞mtDNA A3243G点突变筛查、血乳酸检测和神经影像学等检查。A3243G点突变阳性病例中选取符合MELAS临床疑似诊断标准的患儿（突变阳性组），对其家系进行调查，采集家族成员血进行mtDNA A3243G点突变筛查；A3243G点突变阴性病例中选取符合MELAS临床疑似诊断标准的患儿行肌肉病理活检和肌肉A3243G点突变筛查（突变阴性组）。分析比较两组的临床资料及MELAS遗传学特征。结果 研究期间共有272例疑似线粒体脑肌病的患儿进行了外周血白细胞A3243G点突变的筛查。A3243G点突变的20例阳性标本中，突变均为异胞质性（heteroplasmy），18例符合MELAS的临床疑似诊断标准。血细胞中突变型mtDNA的比例为9.0%～50.0%，其中4例同时在肌肉组织检测到相同突变，突变比例为42.4%～64.8%。临床症状以惊厥、乏力、智力进行性倒退、发热、呕吐、视力障碍和失语为主，身材矮小和体毛增多为主要体征，13例合并癫，血乳酸均升高，头颅CT/MRI显示双侧对称性苍白球钙化和脑梗死信号。A3243G点突变筛查阴性标本中有4例临床符合MELAS临床疑似诊断标准，肌肉病理可见破碎红边纤维，肌肉A3243G点突变筛查阴性。14个家庭中的37名家庭成员采集了外周血进行mtDNA A3243G点突变筛查，突变阳性组中患儿母亲5名检测到A3243G点突变，突变比例分别为3.0％，5.0%，11.8%，21.3% 和26.9%，同胞兄弟4名检测到A3243G突变，突变比例分别为19.3％、33.3%，37.5％和41.5%，均无临床症状，其他成员未检测到突变。本研究A3243G点突变比例与发病年龄和就诊年龄呈负相关趋势，与病程未见相关性。结论MELAS综合征的临床表现复杂多样，线粒体A3243G点突变是我国儿童MELAS最常见的突变，母系遗传为主。突变比例与年龄有相关趋势，与病程未见相关，血A3243G突变检查不能代替肌肉病理诊断。

The studies on clinical and molecular genetic features of MELAS

Objective The aim was to study the clinical characteristics, diagnostic standards and genetic features of MELAS and try to find the association between the A3243G mtDNA mutation rate and clinical phenotypes.Methods PCR RFLP for screening the heteroplasmic A to G transition at nucleotide 3243 of the mitochondrial tRNALeu(UUR) of blood cells and muscle, neuroradiological examination, blood level of lactic acid and muscle biopsy analyses were performed on the 272 patients suspected to be with MELAS in Beijing Children′s Hospital，the Capital Medicine University, during the years of 2001 2008. Eighteen patients with molecular genetic abnormalities of mitochondrial DNA A3243G mutation were taken as the gene diagnosis group for MELAS. Four patients with ragged red fibers on muscle biopsy specimens and with the absence of A3243G mutation were taken as the pathology diagnosis group for MELAS. Comparisons of clinical, laboratorial and neuroradiologic features between two groups were performed. The A3243G point mutation in the mtDNA of blood cells was also detected in some of their parents, maternal relatives(mother and siblings) by using PCR RFLP.ResultsEighteen patients showed heteroplasmy with a mutant load of mtDNA A3243G mutation ranging from 9.0% to 50.0% in blood cells and from 42.4% to 64.8% in muscle tissues in 4 of them. The main clinical features were characterized by epilepsy,exercise intolerance, progressive dementia, fever, vomiting,vision loss, short stature and hypertrichosis on back. Stroke like episodes were found in 7 patients. Laboratory studies revealed elevated serum lactate with levels at 4.2-10.8 mmol·L-1. Cranial CT scan showed calcifications in the bilateral basal ganglia in 9 cases and MRI showed infarct like lesions in 11 cases, involving the lateral temporal occipital and parietal lobes in 6 cases, the bilateral parietal occipital lobes in 4 cases, the frontal lobes in 2 cases. The A3243G point mutation in the mtDNA of blood cells was detected in 37 persons from 14 families. The study showed the A3243G mutation was found in 5/10 of the mothers, the mutation rates were 3.0％, 5.0%,11.8%, 21.3% and 26.9%, respectively, and in 4/7 of the siblings 19.3％,33.3%,37.5％ and 41.5%, respectively, all of them were asymptomatic.Conclusions MELAS was the most common maternally inherited mitochondrial disease with various clinical phenotypes and A3243G mutation of the mtDNA accounted for most MELAS in Chinese children. The proportion of mutant mtDNA was not related to the course of the disease but to the age.