摘要
目的：佩-梅病（Pelizaeus–Merzbacherdisease，PMD）是一种罕见的X连锁隐性遗传弥漫性脑白质髓鞘形成障碍性疾病，1885年德国PelizaeusF.最先描述此病临床表现，1910年德国MerzbacherL发现本病的X连锁隐性遗传特征，且镜检中发现脑白质中髓鞘丢失。PMD属于蛋白脂蛋白1（proteolipidproteinl，PLP1）相关的遗传性髓鞘形成障碍疾病谱中的一种，在脱髓鞘一类疾病中，PMD约占6.6%。临床主要表现为眼球震颤、四肢麻痹、共济失调、运动发育迟缓等，确切发病机制尚未阐明。本研究旨在收集并分析1例PMD患儿家系的临床特征以及PLP1基因的突变，初步探讨基因型与表型的关系，并为PMD患儿家庭提供准确的遗传咨询，为产前诊断提供确切的实验依据。
方法：收集先证者及其家系成员的临床资料，采用多重连接依赖的探针扩增（MLPA）方法，进行PLP1基因突变检测，确定基因突变类型为非重复突变，并且应用PCR方法对PLP1基因的所有7个外显子及内含子连接区域进行扩增，采用DNA直接测序与DNA限制性内切酶方法进行PLP1基因突变检测，并确定基因点突变的位点，分析基因型与表型的关系。
结果：1、临床特点患儿男性，2004年8月出生，生后即发现身体软伴有水平眼震，发育落后，但仍有缓慢进步，6岁8个月时仍不能竖头、翻身、独坐、独走与伸手抓物，智力落后，无惊厥发作。就诊时（6岁8个月）查体：一般检查未见异常。无特殊外貌，水平眼球震颤，余颅神经检查未见异常。四肢有主动运动，无手足徐动。四肢肌力Ⅱ~Ⅳ级，肌容积减少，肌张力低，膝腱反射对称引出，双侧巴氏征阳性。头颅MRI示：大脑半球、小脑、脑干白质弥漫性T2高信号，显示脑白质发育落后，髓鞘形成不良，类似新生儿期头颅MRI表现。本家系中5代56人中除了先证者之兄以外还有11例发病，均为男性，症状与先证者类似。
2、基因突变分析本研究中PLP1基因检测结果发现先证者（V:4）存在第2外显子c.96C>G(p.F32L)的半合子改变，先证者之母（IV:15）、外祖母（III:20）与曾外祖母（II:7）存在与先证者相同的c.96C>G(p.F32L)杂合改变，为表型正常的携带者。结论：1、本例患儿具有水平眼震，发育落后，肌张力变化与头颅MRI特征性改变，符合PMD临床诊断标准。
2、本例PMD患儿PLP1基因突变分析发现了1种核苷酸改变[c.96C>G(p.F32L)]，且在表型正常的先证者之母、外祖母及外曾祖母均携带该核苷酸的改变，其父和大姨、二姨的基因型及表型均正常。该改变为未报道的新突变。本研究扩大了PLP1基因突变谱。c.96C>G(p.F32L)可能成为中国PMD患儿的热点突变。
3、在本例患儿中发现的PLP1基因点突变，可为该患儿及其家庭提供准确的遗传咨询和产前诊断。
Objective:Pelizaeus-Merzbacher disease (PMD) is a rare x-linked recessive genetic diffuse brain white matter myelination barrier disease, In1885, Germany Pelizaeus F. initial described the clinical manifestations of this disease, In1910,Germany Merzbacher L found the characteristics which is x-linked recessive genetic, and there was dysmyelinating in white matter by microscope, PMD is one of the proteolipid protein1(PLP1) related genetic myelination obstacles spectrum of disease, In demyelinated diseases, PMD about6.6%. The symptoms including nystagmus, limbs paralysis, ataxia, motor delays, etc. The exact mechanism has not been elucidated. This study aims to collect and analysis the clinical features in a PMD children's family line, and the mutations of PLP1gene. This study preliminary discuss the relationship between genotype and phenotype, and provide the accurate genetic consultation to PMD children's family, offer exact experiment basis to prenatal diagnosis.
Methods:Collect the proband and his family member's clinical data. Detect the PLP1gene mutations by using the multiplex ligation-dependent probe amplification (MLPA) to determine the types of genetic mutations is not duplication, and all7exons and exon-intron boundaries of PLP1gene were amplified by polymerase chain reaction(PCR). Detect the PLP1gene mutations and confirm where gene point mutants by direct DNA sequencing and DNA restriction enzyme digestion, and analysis the relationship between genotype and phenotype.
Results:(1) Clinical outcomes:Infant is a boy, born in August2004, with weak, horizontal nystagmus, motor delays, but there is still slow progress. There are horizontal nystagmus lower-limb muscle hypertonia; lower-limb knee jerk reflex led; bilateral positive Babinski sign, especially right; bilateral strephenopodia. MRI shows:neonatal white matter myelination. There are13male patients in4-generation of same family line. Infant's brother died in8with similar pathography.
(2) Gene mutation analysis:In this study, the PLP1genetic testing results show that the point mutations occurred in child's PLP1gene. One heterozygous mutations of PLP1were identified c.96C>G (p.F32L) in exon2from proband.The heterozygous change c.96C>G (p.F32L) in exon2was found in the proband's mother、grandmother and grand grandmother with normal phenotype,and the proband's father、two aunts with normal genotype and phenotype.
Conclusions:1. The case suffer from horizontal nystagmus、growth retardation、Muscle tension change、head MRI characteristic changes, which meets the PMD clinical diagnostic criteria.
2. The PLP1gene mutation analysis of this case shows one nucleotide alteration [c.96C＞G (p.F32L)], and the change was found in the proband's mother、grandmother and grand grandmother with normal phenotype, and the proband's father、two aunts with normal genotype and phenotype. This change is a new mutation which is not reported. This research expand the PLP1gene mutation profile. c.96C＞G (p.F32L) likely to be a Chinese PMD children's hot-spot mutation.
3. The PLP1gene point mutation found in this case is able to perform exact genetic counseling and prenatal diagnosis for the proband and his family
引文
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