甲基丙二酸血症伴同型半胱氨酸血症患儿65例的临床及MMACHC基因变异分析

Analysis of clinical phenotypes and MMACHC gene variants in 65 children with Methylmalonic acidemia and homocysteinemia

目的利用Sanger测序对65例甲基丙二酸血症伴同型半胱氨酸血症家系的MMACHC基因进行变异分析,总结其基因变异和临床特点及转归。方法以2017年4月至2022年4月于郑州大学附属儿童医院(郑州儿童医院)确诊的65例甲基丙二酸血症伴同型半胱氨酸血症患儿为研究对象,收集患儿的临床资料,并用PCR产物直接测序法对先证者及其父母的MMACHC基因进行变异分析。结果65例患儿年龄的中位数为3个月(14 d~17岁),来自新生儿筛查28例(43.08%),有黄疸病史者11例(16.92%),不同程度贫血者9例(13.85%)。临床症状以发育落后为主,其他包括增长缓慢、癫痫、脑积水、嗜睡、喂养困难、运动能力倒退或下降、反复呼吸道感染、贫血、黄疸、呼吸和心力衰竭、脑积水、肢体乏力、高血压等。血尿串联质谱筛查提示,甲基丙二酸、丙酰肉碱、丙酰肉碱/乙酰肉碱比值、丙酰肉碱/游离肉碱比值存在不同程度的升高,所有患儿的血同型半胱氨酸均存在升高。65例患儿的变异检出率为98.46%(128/130),共检出22种MMACHC基因变异,最常见者为c.609G>A(W203X)(58/128)、c.658-660del(K220del)(19/128)和c.80A>G(Q27A)(16/128),发现2种新变异:c.565C>T(p.R189C)、c.624_625delTG(p.A208Afs),根据美国医学遗传学与基因组学学会(ACMG)相关指南分别判定为可能致病性变异(PM2_Supporting+PM3+PP2+PP3)和致病性变异(PVS1+PM2_Supporting+PM3+PP2)。变异频率最高的为第4外显子。结论MMACHC基因变异的检出明确了患儿的致病原因,其中c.609G>A变异出现频率最高。发现的2种新变异扩展了MMACHC基因的变异谱。

ObjectiveTo carry out Sanger sequencing for MMACHC gene variants among 65 Chinese pedigrees affected with combined methylmalonic aciduria and homocysteinemia,and summarize their genetic and clinical characteristics and prognosis.MethodsClinical characteristics of the 65 children identified with Methylmalonic acidemia and homocysteinemia at the Children′s Hospital Affiliated to Zhengzhou University(Zhengzhou Children′s Hospital)from April 2017 to April 2022 were selected as the study subjects.Potential variants of the MMACHC gene were detected by direct sequencing of the PCR products.ResultsThe median age of the 65 children was 3 months(14 days to 17 years old).These included 28 cases(43.08%)from neonatal screening,11 cases(16.92%)with a history of jaundice,and 9 cases(13.85%)with various degrees of anemia.The main clinical symptoms included development delay,slow growth,epilepsy,hydrocephalus,lethargy,feeding difficulty,regression or decline in motor ability,recurrent respiratory infections,anemia,jaundice,respiratory and heart failures,hydrocephalus,limb weakness,and hypertension.Blood and urine tandem mass spectrometry screening has revealed increase of methylmalonic acid,propionyl carnitine,propionyl carnitine/acetylcarnitine ratio,and propionyl carnitine/free carnitine ratio to various extents,and blood homocysteine was increased in all patients.The detection rate of genetic variants was 98.46%(128/130),and in total 22 types of MMACHC gene variants were detected.The most common ones have included c.609G>A(W203X)(58/128),c.658-660del(K220del)(19/128),and c.80A>G(Q27A)(16/128).Two novel variants have been identified,namely c.565C>T(p.R189C)and c.624_625delTG(p.A208Afs),which were respectively predicted as likely pathogenic(PM2_Supporting+PM3+PP2+PP3)and pathogenic(PVS1+PM2_Supporting+PM3+PP2)based on the guidelines from the American College of Medical Genetics and Genomics(ACMG).Exon 4 had the highest frequency for the detection.ConclusionIdentification of MMACHC gene variants has confirmed the diagnosis in the children,among which the c.609G>A variant has the highest frequency.Discovery of the new variants has enriched the mutational spectrum of the MMACHC gene.