Molecular genetics of Pelizaeus-Merzbacher disease

描述(申请人提供)：Pelizaeus-Merzbacher病(PMD)是一种X连锁脑白质营养不良症，由编码主要中枢神经系统髓鞘蛋白的蛋白脂蛋白1基因(PLP1)的遗传缺陷引起。含有PLP1的基因区域重复是PMD最常见的原因，占PMD的60%以上。尽管疾病的严重程度可能存在差异，即使在一个单一的家庭中，大多数PLP1重复的患者在出生后的头几个月都有类似的表型，出现眼球震颤和低眼压，在第一个十年出现肢体和步态共济失调、痉挛四肢瘫痪以及认知和视觉障碍。大多数患者的运动里程碑和语音也会延迟。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不是很清楚。在我们之前对13例PMD患者的重组连接DNA序列的研究中，我们发现了与导致基因复制的耦合同源和非同源重组机制一致的数据。然而，Lupski和他的同事最近从对2名有复杂重排的患者的重组连接的分析中提出，这一过程可能也涉及基于复制的机制。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组合策略来分析更大规模的基因复制患者队列中重组断裂点的结构和序列。此外，为了进一步了解这些复杂基因复制导致的临床表型基础，我们将构建一个包含X染色体PLP1区域大量复杂复制的PMD小鼠模型。含有这种复制的ES细胞已经被构建，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，复制编码的基因的表达，包括PLP1，以及髓鞘形成程序中其他基因的表达。X染色体重排部分的分离也将在女性携带者身上进行检查，以确定其对X染色体失活的影响。综上所述，这些研究将为PMD的基因复制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。我们的团队尤其准备好进行这些研究，因为我们开发了独特的患者资源，以及我们在过去十年中对PMD诊断和研究的承诺获得了专业知识。具体目的是：(1)检验PMD患者基因组重排经常发生为复杂重排的假设，包括第二个重复区域和缺失、三重或倒置区域，符合耦合的同源和非同源重组机制。(2)检验Plp1基因复制改变Plp1基因表达的假设，从而导致男性髓鞘程序中断和女性X染色体失活模式的补偿性倾斜。公共卫生相关性：这项研究与公共健康直接相关，因为它将导致更好地了解遗传病的机制，最终将改进PMD和其他由复杂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.