摘要
佩-梅病(Pelizaeus-Merzbacher disease,PMD)是一种罕见的X连锁隐性遗传性白质脑病,美国PMD患病率约1/300,000～1/500,000,德国报道发病率为0.13/100,000活产婴儿,我国仅见于1997年台湾学者的一篇相关报道。临床以眼震、肌张力低下、运动智力发育落后及共济失调为主要表现。该病由位于Xq22.2的蛋白脂蛋白1(proteolipid protein1,PLP1)突变所致,突变类型多样,其中50%～70%为重复突变。佩梅样病(Pelizaeus-Merzbacher-like disease,PMLD)是一种常染色体隐性遗传病,临床表现和PMD患者相似,其致病基因为缝隙连接蛋白a12(Gap Junction Protein a12,GJA12),本基因于2004年定位于1q41,目前在PMLD患者中有数个GJA12基因突变的报道。
目的:在北京大学第一医院儿科收集并分析8例受试对象的临床特征,进行PLP1及GJA12基因突变分析,初步探讨基因型与表型的关系,并为PMD及PMLD患者的确诊、遗传咨询及产前诊断打下基础。
方法:在北京大学第一医院儿科收集8例(男7例、女1例)研究对象及其家系成员的临床资料,对临床症状、体征与影像学特点进行分析。采集外周血5ml提取DNA,采用多重连接依赖的探针扩增(multiple ligation-dependent probe amplification,MLPA)技术检测PLP1基因重复突变,运用DNA直接测序的方法进行PLP1及GJA12基因突变分析,明确基因突变类型,进一步分析基因型与表型的关系。此部分工作均在北京大学第一医院儿科研究室完成。
结果:
1.8例纳入的患者均表现为眼球震颤、运动智力发育落后、头颅MRI显示为髓鞘发育落后,其中7例男性患者临床诊断为先天型(1例)、中间型(3例)、经典型(3例)PMD,1例女性患者为PMLD。
2.7例PMD患者(P1-7)中,P1-5为PLP1基因的重复突变,他们的母亲为PLP1基因重复突变的携带者;在P2大家系中检出另2个(Ⅲ:3 andⅢ:4)表型正常女性PLP1基因重复突变携带者;P6存在PLP1基因第4外显子c.517C＞T(p.P173S)的错义突变,患儿母为携带者。
3.P7未发现PLP1基因及GJA12基因的突变。
4.P8存在GJA12基因c.216delGinsAA的移码突变,患儿父为c.216delGinsAA杂合改变,而母亲正常;与香港遗传学中心合作进行了单亲二倍体的检测,发现此改变为来自父源1号染色体单亲二倍体所致。因此从基因水平确诊为PMLD患者。
结论:
1.建立了PMD的PLP1基因诊断方法,并在国内首次用MLPA技术确诊了5例患者,直接测序方法诊断1例患者;对一个4代大家系进行携带者的检出,发现了3例女性携带者。
2.建立了GJA12基因诊断方法,并在国内首次确诊了1例PMLD患者;发现患儿携带的致病基因均来自父亲1号染色体的单亲二倍体。
Pelizaeus-Merzbacher disease(PMD)is a rare x-linked recessive disorder presenting with nystagmus,impaired motor development,ataxia,and progressive spasticity.In the USA,the prevalence of PMD is estimated to be about 1/300,000 to 1/500,000.The main cause of PMD is alterations of the proteolipid protein 1(PLP1)gene.The PLP1 gene is located on chromosome Xq22.2.Duplication of the PLP1 gene is the most frequent gene defect,accounting for 50-70% of PMD cases,whereas point mutations in the coding sequence or affecting splice sites account for 10-25%of PMD cases.Pelizaeus-Merzbacher-like disease(PMLD)is an autosomal recessive syndrome characterized by early-onset nystagmus,delayed motor milestones,ataxia, progressive spasticity,partial seizures,mild peripheral neuropathy and diffuse leukodystrophy on MRI.It was caused by mutations in the GJA12 gene that encodes connexin 46.6.GJA12 gene was first mapped to 1q41 in 2004 and few of mutations were reported until now.
Objectives The aims of present study were confirmed the clinical diagnosis and clarified the genotype-phenotype correlations in patients with PMD and PMLD by analyzing clinical data and changes of PLP1 gene and GJA12 gene.In addition genetic counseling and prenatal would been available for the family having probands using the results of this study.These datas collected from Peking University of First Hosipital.
Methods 8 patients(male 8,female 1)and their parents as well as 14 family members of patient 2 were included in this study.Clinical data and DNA samples were collected from all the objects.Multiplex ligation-dependent probe amplification(MLPA)assays were performed to detect PLP1 duplication and the sequence analysis were used for alternations of PLP1 gene and GJA12 gene.These datas collected from Peking University of First Hosipital and these works all done at Peking University of First Hosipital.
Results
1.In 8 patients,they were diagnoses as three transitional,three classical,one connatal PMD and one PMLD according to the clinical and radiological criteria..
2.PLP1 duplication was identified in patients 1-5 and their mothers were carriers.In P2' family,another 2 females(Ⅲ:3 andⅢ:4)with normal phenotype were proved to be carriers with PLPlduplication.A missense mutation in exon 4 of PLP1 gene[c.517C＞T(p.P173S)1 was found in patient 6 and his mother was carrier.
3.None change about PLP1 and GJA12 gene was found in patient 7.
4.In patient P8,a c.216delGinsAA homozygous frameshift mutation was identified in exon 2 of GJA12 gene.Her father was heterozygote in this site,but her mother was normal. Moreover,uniparental disomy was found 1q in this patient and originated from her father through collaborated with the Clinical Genetic Service of Hong Kong.
Conclusion
1.The molecular diagnosis of PLP1 and GJA12 genes for PMD and PMLD patients has been set up in China,respectively.
2.This is the first report to diagnosis PMD patients clinically and genetically in China,in which there were five using MLPA assay and one by DNA indirect sequencing.Three female carriers have been found in a four-generation family.
3.One PMLD patient was diagnoses through analyzing GJA12 gene novel mutation and confirmed this mutation was uniparental disomy in 1 chromosome originated from her father. This is the first report in China.
引文
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