Exome re-sequencing candidate loci for familial essential tremor

描述（由申请人提供）：特发性震颤（ET）是人类最常见的神经系统疾病之一，患病率几乎达到4%。ET作为显性性状遗传，在大多数家族病例中具有不完全外显率，但复杂的多基因遗传是可能的。家族性ET的三个遗传易感位点存在于染色体3p13.1 （ETM1）、2p24 （ETM2）和6p23 （ETM3）上，但在与这些位点相关的家族中尚未发现致病基因。16个冰岛家族的多态ETM1位点和23个法国家族的多巴胺受体D3基因变异与ET表型相关。ETM2基因座与四个美国家庭的一种疾病等位基因有关。进一步的研究表明，在美国、新加坡和韩国的人群中，ETM2和ET表型之间存在密切的等位基因关联。两个北美家族与ETM3位点有关，其中最大的家族表现出混合表型，除了ET外还包括肌张力障碍。由于表型的存在，不完全外显率和ET的高患病率，遗传模式不明确，阻碍了对因果基因的寻找。固相微阵列和仪器技术的进步通过允许大规模DNA测序部分地缓解了这些障碍。基因组生物信息学的进步和经过验证的规范种群数据库的可用性（例如1000基因组SNP数据库，dbSNP和HapMap）提供了从假定突变中过滤遗传变异的能力。利用这项技术，我们最近通过对4.2兆碱基（Mb）候选区域的高密度测序，在三个不相关的家族中发现了一个新的基因——猫白血病病毒亚群C受体1基因的错义突变，该基因是孟德尔疾病、后柱共济失调和视网膜色素变性的原因。这一发现证实了我们在开展拟议的遗传研究所需的所有特定技术方面的专业知识，并为specific Aim 1提供了原理证明，即使用高通量重测序技术在与ETM2和ETM3位点相关的两个大而信息丰富的家族中识别导致ET的基因。我们为24.6 Mb ETM2（48,054个鱼饵）和14.4 Mb ETM3（30,796个鱼饵）基因座设计了一个120碱基对鱼饵长度的鱼饵库，包括所有的调控区域、外显子、剪接位点、增强子和保守的基因间区域。功率分析估计，检测具有95%置信的突变所需的样本量是来自与ETM2和ETM3位点相关的每个家族的10个具有疾病单倍型的受影响个体和10个没有疾病单倍型的未受影响个体。Sanger测序将再次确认来自两个家族的20名受影响个体中发现的ETM2和ETM3突变。这些候选基因将在另外73个不相关的ET家族中进行Sanger测序，以确定其他ETM2和ETM3突变。未来的体外和体内实验将分析ET基因突变在衰老和发育过程中的功能后果。

DESCRIPTION (provided by applicant): Essential tremor (ET) is one of the most common neurological disorders in humans with a prevalence reaching almost four percent. ET is inherited as a dominant trait with incomplete penetrance in most familial cases but complex multi-genic transmission is possible. Three genetic susceptibility loci for familial ET exist on chromosomes 3p13.1 (ETM1), 2p24 (ETM2), and 6p23 (ETM3), but the causal genes have not been identified in the families linked to these loci. Polymorphic ETM1 loci in 16 Icelandic families and a variant in the dopamine receptor D3 gene in 23 French families are associated with an ET phenotype. ETM2 loci are linked to a disease allele in four American families. Further studies suggest a tight allelic association between ETM2 and the ET phenotype in populations from the United States, Singapore, and Korea. Two North American families are linked to ETM3 loci with the largest family showing a mixed phenotype that includes dystonia in addition to ET. An unclear pattern of inheritance due to the presence of phenocopies, incomplete penetrance, and the high prevalence of ET, hinder the search for causal genes. Advances in solid- phase microarrays, and instrumentation have partially alleviated these barriers by permitting large scale DNA sequencing. Advances in genome bioinformatics and the availability of validated normative population databases (e.g. 1000 Genomes SNP database, dbSNP, and HapMap) provide the capability to filter genetic variants from putative mutations. By using this technology, we recently identified missense mutations in a novel gene, feline leukemia virus subgroup C receptor 1 gene, as the cause of the Mendelian disorder, posterior column ataxia and retinitis pigmentosa, in three unrelated families by high density sequencing of the 4.2 megabase (Mb) candidate region. This discovery confirms our expertise in all of the specific technologies required to carry out the proposed genetic studies and provides proof of principle for Specific Aim 1 to identify the genes that cause ET in two large, informative families linked to the ETM2 and ETM3 loci using high- throughput resequencing technology. We have designed a bait tiling library using 120 base-pair bait lengths for the 24.6 Mb ETM2 (48,054 baits) and the 14.4 Mb ETM3 (30,796 baits) loci to include all regulatory regions, exons, splice sites, enhancer, and conserved intergenic regions. A power analysis estimates that the sample size required to detect mutations with 95% confidence are 10 affected individuals with a disease haplotype and 10 unaffected individuals without the disease haplotype from each family linked to the ETM2 and ETM3 loci. Sanger sequencing will reconfirm the ETM2 and ETM3 mutations identified in the 20 affected individuals from the two families. These candidate genes will be Sanger sequenced in 73 additional, unrelated families with ET to identify other ETM2 and ETM3 mutations. Future experiments using in vitro and in vivo models will analyze the functional consequences of ET gene mutations during aging and development. PUBLIC HEALTH RELEVANCE: The identification of ET genes will improve diagnostic accuracy, refine the classification of tremor, and is a pivotal step toward finding effective treatments. Studying the untoward effects of mutant ET genes will increase our knowledge of ET and other movement disorders such as Parkinson disease.