Modeling TAR Microdeletion Syndrome in Mouse

描述（由申请人提供）： 拷贝数变异（CNV）综合征与低拷贝率代表了一个新的挑战，以了解和预测疾病的表现。一种这样的低转移率CNV综合征是血小板减少性桡骨缺失（TAR）综合征。TAR综合征患者血小板计数低（血小板减少症），可导致危及生命的出血，以及手臂双侧桡骨缺失，导致前臂缩短。染色体1q21.1上200-kb的缺失是导致TAR综合征的必要条件，但不是充分条件。要发生疾病，基因组中其他地方的未知修饰突变必须沿着缺失。虽然1q21.1缺失的发现代表着在解读TAR综合征病因方面向前迈出了一大步，但由于未知的修饰物，诊断预测仍然受到阻碍。此外，200 kb的缺失删除了11个基因，目前还没有已知的TAR综合征的基因型-表型相关性。试图发现人类基因组中的修饰突变是一项艰巨的任务，需要对大量受影响和未受影响的个体进行全外显子组或全基因组测序。小鼠模型具有优势，因为许多描述良好的近交系可用于测试遗传背景的影响，并且遗传资源可用于快速定位和识别修饰突变。本提案的目标是开发TAR综合征的小鼠模型，然后使用该模型确定TAR修饰物的遗传模式，目的如下：1）删除小鼠3号染色体上的同线区，2A）测定携带缺失的小鼠的血小板计数、桡骨损失以及在一些TAR患者中观察到的心脏和肾脏缺陷，和2B）将缺失与具有已知的血小板计数和骨长度变异的近交系杂交，以确定TAR修饰子的遗传模式。在小鼠中，血小板计数和骨长度存在明显和实质性的变化，并且它们是相关的，强烈认为我们选择的品系将具有遗传差异，并将显示表型变异。在本提案结束时，我们将能够映射和识别TAR修饰符，这将通过允许有针对性的诊断测试和更精确的复发风险估计来产生直接的临床影响。我们的新实验方法可以作为一个通用模型，快速有效地识别与人类疾病相关的基因组变异。 公共卫生相关性： 血小板减少性桡骨缺如（TAR）综合征的特征是血小板计数低，可导致危及生命的出血，以及前臂桡骨缺如。TAR部分是由1号染色体的一部分缺失引起的，该部分缺失了11个基因，但还必须发生额外的未知突变才能引起疾病。为了更好地了解TAR综合征的遗传和原因，我们建议在几种不同的近交系小鼠品系上制作携带相同缺失的小鼠模型，使我们能够最终找到未知的突变。

DESCRIPTION (provided by applicant): Copy number variation (CNV) syndromes with low penetrance represent a new challenge to understanding and predicting disease manifestation. One such low-penetrance CNV syndrome is Thrombocytopenia-absent radius (TAR) syndrome. Patients with TAR syndrome have low blood platelet counts (thrombocytopenia), which can lead to life-threatening hemorrhage, as well as bilateral absence of both radius bones in the arm, resulting in shortened forearms. A 200-kilobase (kb) deletion on chromosome 1q21.1 is necessary, but not sufficient, to cause TAR syndrome. To develop disease, an unknown, modifying mutation elsewhere in the genome must be present along with the deletion. While the discovery of the 1q21.1 deletion represented a huge step forward in deciphering the etiology of TAR syndrome, diagnostic predictions are still hindered due to the unknown modifier. In addition, the 200-kb deletion removes 11 genes, and there are currently no known genotype-phenotype correlations for TAR syndrome. Attempting to discover modifying mutations in the human genome is a daunting task, requiring whole-exome or whole-genome sequencing of large numbers of affected and unaffected individuals. Mouse models have an advantage because many well-described inbred strains are available to test the effect of genetic background, and genetic resources are available to quickly map and identify modifying mutations. The goal of this proposal is to develop a mouse model for TAR syndrome and then use the model to determine the inheritance pattern of the TAR modifier, through the following aims: 1) delete the syntenic region on mouse chromosome 3, 2A) assay deletion-carrying mice for blood platelet count, loss of radius bones, and heart and renal defects observed in some TAR patients, and 2B) cross the deletion onto inbred strains with known variation in blood platelet count and bone length to determine the inheritance pattern of the TAR modifier. There is clear and substantial variation in both blood platelet count and bone length in mouse, and they are correlated, arguing strongly that the strains we choose will harbor genetic differences and will show phenotypic variation. At the end of this proposal we will be in position to map and identify the TAR modifier, which will have an immediate clinical impact by allowing targeted diagnostic testing and much more precise recurrence risk estimates. Our novel experimental approach can serve as a general model to quickly and efficiently identify genomic variation that is relevant to human disease. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE Thrombocytopenia-absent radius (TAR) syndrome is characterized by low blood platelet counts, which can cause life-threatening hemorrhage, and absence of the radius bones in the forearm. TAR is partially caused by a deletion of part of chromosome 1 that removes 11 genes, but an additional, unknown mutation must also occur to cause disease. To better understand the inheritance and cause of TAR syndrome, we propose to make a mouse model carrying the same deletion on several different inbred mouse strains, allowing us to eventually find the unknown mutation.