Genetic Basis of Birth Defects in 22q11 Deletion Syndrome

22q11.2缺失综合征（22q11DS），也被称为velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS)，是人类最常见的微缺失疾病之一，发生率为1/ 4000活产婴儿。超过90%的患者有典型的3mb（百万碱基对）缺失，而一些患者有较小的缺失。临床特征包括心血管缺陷、免疫、颅面异常、精神疾病和轻度智力低下。尽管少数候选基因已被确定并自行研究，但有重要证据表明，其他基因对整体表型有贡献。例如，在3mb区域的近端（着丝粒）一半被称为TBX1的基因和远端一半被称为CRKL的基因被发现在心血管发育中具有遗传相互作用。最近，在3mb区域发现了与该综合征相关的非重叠缺失，提示不同基因的单倍性不足可能导致相关的先天性畸形。近端1.5 Mb区域的几个基因是神经认知缺陷的候选基因，但远端一半的基因尚未被研究。最后，这种疾病的表现是可变的，可能是由于剩余等位基因上的基因序列变异。了解基因功能和相互作用有助于深入了解VCFS/DGS的分子发病机制。我们的假设是22q11.2区域内连续基因的单倍不足是导致该疾病整体表型的原因。22q11.2上的基因在小鼠16号染色体上保守。产生了包含22q11.2区域近半的1.5 Mb的缺失，并对其进行了表征，但没有产生相当于3 Mb的缺失，这主要是由于小鼠基因图谱过去的模糊性。在Specific Aim 1中，我们将使用Cre/loxP系统（MICER）创建一个缺失，该缺失包括人类中大多数半合子基因，具有典型的3mb缺失。这些老鼠应该能重现人类的状况。在Specific Aim 2中，我们将比较先前产生1.5 Mb缺失的小鼠，Tbx1和Crkl小鼠之间的表型。Aim 2中的研究将直接检验我们的假设。下一个目标将是通过创建具有重叠的较小缺失和重复的额外等位基因来执行基因型表型相关性，这将在未来完成。我们也对建立互惠的3mb重复综合征dup(22)（q11.2, q11.2）的模型感兴趣，并且具有重复的小鼠可以达到此目的。

DESCRIPTION (provided by applicant): Mouse genomic engineering for 22q11.2 rearrangement disorders The 22q11.2 deletion syndrome (22q11DS), also known as velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS), is one of the most common microdeletion disorders in humans, occurring in 1/4,000 live births. Over 90% of patients have a typical 3 Mb (million base pair) deletion, while some have smaller deletions within. The characteristic clinical features include cardiovascular defects, immune, and craniofacial anomalies as well as psychiatric illness and mild mental retardation. Although a handful of candidate genes have been identified and pursued on their own, there is significant evidence that additional genes contribute to the overall phenotype. For example, a gene in the proximal (centromeric) half of the 3 Mb region, termed TBX1, and distal half, termed CRKL have been found to genetically interact for cardiovascular development. Recently, it was found that non-overlapping deletions within the 3 Mb region have been identified in association with the syndrome, suggesting that haploinsufficiency of different genes can contribute to related congenital malformations. Several genes in the proximal 1.5 Mb region are candidates for neurocognitive deficits, but genes in the distal half have not been pursued as of yet. Finally, the disorder occurs with variable expressivity, possibly due to sequence variation in genes on the remaining allele. Understanding gene functions and interactions would provide insights into the molecular pathogenesis of VCFS/DGS. Our hypothesis is that haploinsufficiency of contiguous gene(s) within the 22q11.2 region is responsible for the overall phenotype of the disorder. The genes on 22q11.2 are conserved on mouse chromosome 16. A 1.5 Mb deletion comprising the proximal half of the 22q11.2 region was generated and characterized, but a deletion that is equivalent to the 3 Mb deletion was not made, largely due to past ambiguities in the mouse gene map. In Specific Aim 1, we will use the Cre/loxP system (MICER) to create a deletion that includes most of the genes hemizygous in humans with the typical 3 Mb deletion. These mice should recapitulate the human condition. In Specific Aim 2, we will compare the phenotypes between mice with the 1.5 Mb deletion that was previously generated, Tbx1 and Crkl mice. The studies in Aim 2 will directly test our hypothesis. The next goal would be to perform genotype phenotype correlations by creation of additional alleles with overlapping smaller deletions and duplications and this will be done in the future. We are also interested in modeling the reciprocal 3 Mb duplication syndrome, dup(22)(q11.2, q11.2) and the mice with the duplication can serve this purpose. PUBLIC HEALTH RELEVANCE: We propose to generate a mouse model of velo-cardio-facial/DiGeorge syndrome to test the hypothesis that it results from haploinsufficiency of contiguous genes on 22q11.2.