Molecular genetics of Pelizaeus-Merzbacher disease

描述（由申请人提供）：Pelizaeus-Merzbacher病（PMD）是由编码主要中枢神经系统髓磷脂蛋白的蛋白脂蛋白1基因（PLP1）的遗传缺陷引起的x连锁白质营养不良。包含PLP1的基因区域的重复是PMD最常见的原因，占60%以上的病例。尽管疾病的严重程度可能存在差异，即使在同一个家族中，大多数PLP1重复的患者具有相似的表型，在出生后的头几个月出现眼球震颤和张力低下，在头十年出现肢体和步态共济失调、痉挛性四肢瘫以及认知和视力障碍。在大多数患者中，运动里程碑和语言也会延迟。无论是基因复制的分子机制还是PMD临床表型的分子基础都没有得到很好的理解。在我们之前对13例PMD患者的重组连接DNA序列的研究中，我们发现了导致基因重复的耦合同源和非同源重组机制。然而，Lupski及其同事最近通过对2例复杂重排患者的重组连接的分析表明，基于复制的机制可能也参与了这一过程。在拟议的研究中，我们将使用包括高密度寡核苷酸阵列在内的多种策略，在更大的基因重复患者队列中分析重组断点的结构和序列。此外，为了进一步了解这些复杂基因重复引起的临床表型的基础，我们将构建含有x染色体PLP1区域大量复杂重复的PMD小鼠模型。含有这种重复的胚胎干细胞已经被构建，并且正在制造含有x染色体重排部分的小鼠。然后将分析动物的临床表型，由复制编码的基因的表达，包括PLP1，以及髓鞘形成程序中的其他基因的表达。X染色体重排部分的分离也将在女性携带者中进行检查，以了解其对X失活的影响。综上所述，这些研究将为PMD中基因复制的机制以及这种基因复制对基因表达和神经功能的影响提供重要的新信息。由于我们开发的独特患者资源以及我们在过去十年中对PMD诊断和研究的承诺所获得的专业知识，我们的团队特别准备好进行这些研究。具体目的是：(1)验证PMD患者基因组重排经常以复杂重排的方式发生的假设，包括第二个重复区域和删除，三次重复或倒置区域，符合耦合的同源或非同源重组机制。(2)为了验证Plp1位点基因重复的存在改变了Plp1基因的表达，导致雄性髓磷脂程序中断和雌性x染色体失活模式的代偿性扭曲的假设。公共卫生相关性：这项研究与公共卫生直接相关，因为它将导致对遗传疾病机制的更好理解，这将最终改善PMD和其他由复杂的基因组和基因突变事件引起的疾病的诊断和治疗方法。

DESCRIPTION (provided by applicant): Pelizaeus-Merzbacher disease (PMD) is an X-linked leukodystrophy caused by genetic defects of the proteolipid protein 1 gene (PLP1) that encodes the major central nervous system myelin protein. Duplication of a gene region containing PLP1 is the most common cause of PMD, accounting for over 60% of cases. Although there can be variability in the severity of the disease, even within a single family, most patients with PLP1 duplications have a similar phenotype with onset of nystagmus and hypotonia in the first months of life, and limb and gait ataxia, spastic quadriparesis, and cognitive and visual impairment during the first decade. Motor milestones and speech are also delayed in most patients. Neither the molecular mechanisms of gene duplication nor the molecular basis for the clinical phenotype in PMD is well understood. In our previous studies of the DNA sequences of recombinant junctions in 13 patients with PMD, we have found data consistent with a coupled homologous, nonhomologous recombination mechanism causing the gene duplications. Lupski and co-workers, however, recently suggested from the analysis of recombinant junctions in 2 patients with complex rearrangements that a replication-based mechanism may also be involved in this process. In the proposed studies, we will analyze the structure and sequence of the recombination breakpoints in a larger cohort of patients with gene duplications using a combination of strategies, including high-density oligonucleotide arrays. In addition, to further understand the basis of the clinical phenotype caused by these complex gene duplications, we will construct a mouse model of PMD containing a large, complex duplication of the PLP1 region of the X-chromosome. ES cells containing this duplication have been constructed, and mice containing the rearranged portion of the X-chromosome are being made. Animals will then be analyzed for their clinical phenotype, the expression of genes encoded by the duplication, including PLP1, as well as expression of other genes in the program of myelination. Segregation of the rearranged portion of the X- chromosome will also be examined in female carriers for its effects on X-inactivation. Taken together, these studies will provide important new information on the mechanism of gene duplication in PMD, as well as the effect of this gene duplication on gene expression and neurological function. Our group is particularly well poised to perform these studies because of the unique patient resource we have developed and the expertise we have gained from a commitment to PMD diagnostics and research during the past decade. The specific aims are: (1) To test the hypothesis that genomic rearrangements in PMD patients frequently occur as complex rearrangements, including a second duplicated region and deleted, triplicated or inverted regions, consistent with a coupled homologous, nonhomologous recombination mechanism. (2) To test the hypothesis that the presence of a gene duplication at the Plp1 locus alters Plp1 gene expression leading to disruption of the myelin program in males and compensatory skewing of the X-chromosome inactivation pattern in females. PUBLIC HEALTH RELEVANCE: This research is directly relevant to public health because it will lead to a better understanding of genetic disease mechanisms, which will ultimately improve diagnostic and therapeutic approaches for PMD and other disorders that result from complex genomic and genetic mutational events.