Molecular Analysis of Xq28-Linked Incontinentia Pigmenti

描述（由申请人提供）：色素失禁症（IP）是一种X连锁显性和男性致命疾病，主要影响皮肤、牙齿、眼睛和中枢神经系统。女性存活是因为表达正常X染色体的细胞的选择性增殖，因此，女性中X失活的偏斜是IP的标志性特征。我们最近发现了IP相关的基因，并在多个IP患者中证实了突变。NEMO基因参与NF-κ B信号转导途径，其缺失使细胞易于凋亡。因此，雄性的功能丧失突变导致人类和小鼠的胚胎死亡。虽然Nemo基因敲除模型在雌性小鼠中表现出经典的IP表型，但雄性小鼠在胚胎发育期间死亡。女性IP患者表现出一种表型，可能是因为X-失活模式和表达突变X染色体的细胞凋亡的时间。大多数IP患者携带外显子4-10的缺失，这可能是由于位于内含子3和基因末端的重复序列在重组过程中的错位而发生的。其余患者表现出微缺失、重复和替换。几乎所有的患者都表现出功能缺失突变。虽然IP一直被认为是一个典型的男性致死性疾病，我们最近确定的突变，男性也，这似乎是hypomorphic和不致命的细胞环境。当男性患有IP时，他们会出现与IP通常无关的其他体征。因此，由于先前对经典IP中男性致死性的误解以及存活IP男性中存在非典型体征，许多男性IP病例可能被误认为另一种类似疾病。因此，该项目的目标之一是检查患有类似疾病的患者，以确定他们是否与IP等位。由于亚晶突变引起的变异表型可能揭示NEMO和NF-κ B通路功能的重要信息。在这方面，我们已经提出了创建转基因小鼠表达非致死性，亚型突变，调查的各种功能的NF-κ B途径和发病机制的IP。这些转基因小鼠将有助于解决以下假设：亚晶型突变导致具有残留活性的不稳定蛋白质，并且突变表达的特定时间导致在人类中观察到的表型。作为第三个目标，本项目的重点是通过分析其产品来理解NEMO表达。这一努力有望提供深入了解NEMO表达的控制及其通过NF-κ B途径对下游活性的影响。最后，IP患者的突变检测因位于第一个拷贝远端约75 kb处的NEMO第二个拷贝的存在而变得复杂。这两个拷贝在外显子3和外显子10远端约10 kb之间具有近100%的同源性。第二个拷贝（NEMO）缺少外显子1和2，可能没有功能。因此，本项目的第四个目标是确定这种重复拷贝在IP突变中的作用。总的来说，本项目的目的将有助于了解IP在男性的发病机制，NF-κ B信号通路的调节，NEMO表达的调节，以及两个NEMO拷贝的性质。

DESCRIPTION (provided by applicant): Incontinentia pigmenti (IP) is an X-linked dominant and male-lethal disorder that mainly affects the skin, teeth, eyes, and central nervous system. Females survive because of selective proliferation of cells expressing the normal X chromosome and therefore, skewing of X-inactivation in females is a hallmark feature of IP. We recently identified the gene involved in IP and demonstrated mutations in multiple IP patients. The gene, NEMO, is involved in the NF-kB signal transduction pathway and its absence renders cells susceptible to apoptosis. Hence, loss-of-function mutations in males result in embryonic lethality in humans as well as mice. While knockout models of Nemo demonstrate a classic IP phenotype in female mice, the males die during embryonic development. Female IP patients demonstrate a phenotype presumably because of the X-inactivation pattern and the timing of apoptosis in cells expressing the mutant X chromosome. A majority of IP patients carry a deletion of exons 4-10 that occurs due to misalignment, possibly during recombination, of repeats located in intron 3 and at the end of the gene. The remaining patients have demonstrated microdeletions, duplications, and substitutions. Nearly all of our patients exhibit loss-of-function mutations. Although IP has been considered a classic male-lethal disorder, we recently identified mutations in males also, which appear to be hypomorphic and not lethal to the cellular environment. When males have IP, they present other signs not typically associated with IP. Therefore, numerous male IP cases may have been mistaken for another similar disorder due to previous misconceptions about male lethality in classic IP and the presence of atypical signs in surviving IP males. Hence, one of the goals of this project is to examine patients with similar disorders to see if they are allelic with IP. Variant phenotypes due to hypomorphic mutations are likely to reveal significant information about the functioning of NEMO and the NF-kB pathway. In this respect, we have proposed the creation of transgenic mice expressing nonlethal, hypomorphic mutations to investigate the various functions of the NF-kB pathway and the pathogenesis of IP. These transgenic mice will help address the hypothesis that hypomorphic mutations lead to an unstable protein with residual activity and that the specific timing of expression of the mutation leads to the phenotypes observed in humans. As a third goal, this project focuses on understanding NEMO expression by analyzing its product. This effort is expected to provide insight into the control of NEMO expression and its consequence on downstream activity via the NF-kB pathway. Lastly, mutation detection in IP patients is complicated by the presence of a second copy of NEMO located ~75kb distal to the first copy. These two copies share nearly 100% homology between exon 3 and ~10kb distal to exon 10. The second copy (NEMO) lacks exons 1 and 2 and may not be functional. The fourth goal of this project is, therefore, to determine role of this repeated copy in IP mutation. Collectively, the aims of this project will help understand the pathogenesis of IP in males, the regulation of the NF-kB signaling pathway, the regulation of NEMO expression, and the nature of the two NEMO copies.