Molecular genetics of Pelizaeus-Merzbacher disease

描述（由申请人提供）：Pelizaeus-Merzbacher病（PMD）是一种X连锁脑白质营养不良，由编码主要中枢神经系统髓鞘蛋白的蛋白脂质蛋白1基因（PLP 1）的遗传缺陷引起。 含有PLP 1的基因区域的复制是PMD的最常见原因，占病例的60%以上。 尽管疾病的严重程度可能存在变异性，即使在单个家族中，大多数PLP 1重复的患者也具有相似的表型，在生命的最初几个月内发生眼球震颤和张力减退，在最初十年内发生肢体和步态共济失调、痉挛性四肢轻瘫以及认知和视觉障碍。 大多数患者的运动里程碑和语言也会延迟。 基因复制的分子机制和PMD临床表型的分子基础都还不清楚。 在我们以前的研究中，13例PMD患者的重组接头的DNA序列，我们发现数据一致的耦合同源，非同源重组机制，导致基因复制。 然而，Lupski及其同事最近从2例复杂重排患者的重组连接分析中提出，基于复制的机制也可能参与这一过程。 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的基因重复引起的临床表型的基础，我们将构建一个PMD小鼠模型，该模型包含X染色体PLP 1区域的大的复杂重复。 含有这种复制的ES细胞已经被构建出来，含有X染色体重排部分的小鼠正在制造中。 然后将分析动物的临床表型、由重复编码的基因（包括PLP 1）的表达以及髓鞘形成程序中其他基因的表达。 还将在女性携带者中检查X染色体重排部分的分离对X失活的影响。 总之，这些研究将提供重要的新信息PMD的基因复制的机制，以及这种基因复制对基因表达和神经功能的影响。 我们的团队特别准备好进行这些研究，因为我们开发了独特的患者资源，并且我们在过去十年中从PMD诊断和研究中获得了专业知识。 具体目标是：（1）检验PMD患者的基因组重排经常以复杂重排形式发生的假设，包括第二个重复区域和缺失、三重或倒置区域，与偶联的同源、非同源重组机制一致。 (2)检验Plp 1基因座存在基因重复改变Plp 1基因表达导致男性髓鞘程序中断和女性X染色体失活模式补偿性偏斜的假设。 公共卫生相关性：这项研究与公共卫生直接相关，因为它将导致更好地了解遗传疾病机制，最终改善PMD和其他由复杂基因组和遗传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.