白质消融性白质脑病患儿12例临床与遗传学研究

Genetical and clinical study on twelve Chinese children with leukoencephalopathy with vanishing white matter disease

目的对临床诊断为白质消融性白质脑病(VWM)的中国患儿进行真核细胞翻译启动因子2Bα-ε(eIF2Bα-ε)的相应编码基因(EIF2B1～5)突变分析,以期提高儿科医生对该病的认识。方法选择临床诊断为VWM的患儿为研究对象,分析其临床特征;进行EIF2B1～5基因突变筛查;对新发现的EIF2B5基因突变,在HEK293细胞中进行突变蛋白表达水平分析。结果2006至2008年在北京大学第一医院儿科临床诊断VWM患儿12例,其中男8例,女4例。发病前智力、运动发育正常或轻度落后;起病年龄为1岁6个月至6岁8个月,均亚急性起病,起病症状多为运动功能障碍。随访至2009年6月,病程为9个月至7年。均为病情进展性加重病程,其中7例伴发作性病情加重。头颅MRI检查均提示对称性大脑白质液化特征。共发现EIF2B5,EIF2B3和EIF2B2的16种突变,其中包括9种新突变:7种错义突变为EIF2B5:c.185A>T(p.D62V),c.1004G>C(p.C335S),c.1126A>G(p.N376D);EIF2B3:c.140G>A(p.G47E),c.1037T>C(p.I346T);EIF2B2:c.254T>A(p.V85E),c.922G>A(p.V308M);1种无义突变为EIF2B5:c.805C>T(R269X);1种缺失突变为EIF2B5:c.1827-1838del(p.S610-D613del)。其中EIF2B3突变占所有突变的18.8%(3/16)。蛋白表达水平分析发现EIF2B5基因的p.R296X和p.S610-D613del突变导致eIF2Bε的蛋白表达水平显著降低。结论12例患儿均符合VWM早期儿童型诊断,发现了9种EIF2B1～5的新突变,提示中国VWM患儿具有独特突变谱。新发现的EIF2B5p.R296X和p.S610-D613del突变可导致蛋白功能严重受损。

Objective Vanishing white matter disease,inherited with autosomal recessiveu manner,is supposed to be one of the most prevalent inherited leukoencephalopathy in childhood.It is the first known hereditary human disease due to the direct defects in translation initiation process,with the gene defects in EIF2B1-5,encoding the five subunits of eukaryotic translation initiation factor 2B（eIF2B α,β,γ,δ and ε） identified in 2001 to 2002.The pathogenesis of vanishing white matter disease is still far from well understood.Methods The analysis of clinical features and EIF2B1-5 mutation screening was performed in 12 Chinese children,who fulfilled the diagnostic criteria clinically proposed by van der Knaap.Genomic DNA was extracted from peripheral leukocytes.Mutation screening for EIF2B5 was carried out in each patient firstly,followed by screening for EIF2B4,EIF2B2,EIF2B3 and EIF2B1.For novel EIF2B5 mutations identified,in vitro functional study was carried out in transfected HEK 293 cells.Results These patients,consisting of 8 boys and 4 girls,came from 12 core families.All patients presented with classical phenotypes.All individuals were free of symptoms at birth and their developmental milestones were normal or mildly delayed.The symptoms began to appear from 1 year and 6 months to 6 years and 8 months of age,usually with subacute onset.The initial symptom was usually movement disturbance.The illness course was 9 months to 7 years until the last follow up.In all cases,the disease progressed,and with episodic aggravation in 7 cases.The brain MRI showed symmetric and diffuse abnormal signal in periventricular white matter in all cases,with a part having signal intensity close to cerebrospinal fluid on T1-weighted,T2-weighted and flair images.Sixteen mutations were identified in EIF2B5,EIF2B3 and EIF2B2,consisting of 9 novel mutations and 7 mutations reported previously.Nine novel mutations included 7 missense mutations（EIF2B5：c.185〉AT,p.D62V;c.1004G〉C,p.C335S;c.1126A〉G,p.N376D;EIF2B3：c.140G〉A,p.G47E;c.1037T〉C,p.I346T;EIF2B2：c.254 T〉A,p.V85E;c.922 G〉A,p.V308M）,1 nonsense mutation（EIF2B5：c.805CT,R269X）,and 1 deletion mutation（EIF2B5：c.1827-1838del,p.S610-D613del）.EIF2B3 mutation,accounting for 18.8% of total mutations found in this study,was more prevalent than previous reports in Caucasian population（7%）.A hot spot mutation in EIF2B3 was identified.Further functional study on five novel EIF2B5 mutations revealed that p.R296X and p.S610-D613del mutations resulted in significant loss of the mutant protein.Conclusions Vanishing white matter disease patients with mutations were firstly reported in China.Our study identified 9 novel EIF2B mutations and revealed the unique mutation spectrum in Chinese patients.EIF2B5 mutations,p.R296X and p.S610-D613del,were probably the cause of loss of protein function.Further functional analysis of other mutations is ongoing.