Genetic Basis of Congenital Anophthalmia

描述（由申请人提供）：无眼症、小眼症和结肠畸形（MAC）是先天性缺陷，其中眼睛缺失或非常小，或视神经杯发育过程中脉络膜裂隙无法闭合。大多数病例是散发的，但常染色体隐性，显性和x连锁遗传模式已被描述，通常具有降低外显率。少数基因已发现突变，包括转录因子PAX6、CHX10、RX、SOX2和OTX2，以及生长因子GDF6和BMP4。这些在发育的关键早期阶段表达，当视野建立和视原基扩张时。然而，大多数病例仍然无法解释。我们通过连锁分析在一个大的家系中定义了一个常染色体显性MAC的新位点。我们的目标是细化地图位置，并确定非重组区域的致病突变。我们还在严重双侧小眼或无眼症患儿中发现了PAX6和SOX基因重排的新类别。我们的目标是详细描述这些突变，测试发病机制，并系统地筛选全基因组的MAC患者队列，以寻找相关突变。最后，我们定义了小鼠无眼突变（ey1）的三个修饰子，这是Rx同源盒基因中的一个隐性半胚等位基因，可降低ZRDCT菌株中Rx多肽的丰度，从而创建了一个敏化背景，以识别该动物模型中的其他MAC基因（Tucker et al. 2001）。这些修饰位点（ey2, ey3, ey4）是表达无眼性状所必需的，并且在F2杂交中表现出很强的成对相互作用。已经确定了位置候选基因，包括腹侧视杯形态发生所需的一个基因，以及已知在后生动物中限制视野的Wnt信号通路的两个拮抗剂。我们建议这些修饰因子通过增加头外胚层内Wnt的活性来增强无眼性状的外显率。我们的目标是完善ey2-ey4的定位，并使用特定的靶向突变和条件敲除小鼠来验证这一假设。公共卫生相关性：我们将发现导致出生时眼睛缺失（无眼症）、非常小或严重畸形（结肠瘤）的突变。我们将使用遗传连锁分析来测试多个患病儿童的家系，并将确定这些疾病的分子基础。我们还将测试在实验室小鼠中产生无眼性状的特定基因相互作用。这些研究探索了眼睛形成的最早阶段。我们的研究结果将提高对人眼畸形的诊断和理解，以及出生缺陷背后复杂的遗传因素。

DESCRIPTION (provided by applicant): Anophthalmia, microphthalmia and coloboma (MAC) are birth defects in which the eyes are absent or very small, or where the choroid fissure fails to close during optic cup development. Most cases are sporadic, but autosomal recessive, dominant and X-linked inheritance patterns have been described, often with reduced penetrance. Mutations in few genes have been identified, including transcription factors PAX6, CHX10, RX, SOX2 and OTX2, and growth factors GDF6 and BMP4. These are expressed during critical early stages of development, when the eye field is established and the optic primordia expands. However, most cases remain unexplained. We have defined a new locus for autosomal dominant MAC by linkage analysis in a large pedigree. We aim to refine the map position and identify the causative mutation within the nonrecombinant region. We have also discovered new categories of PAX6 and SOX gene rearrangements in children with severe bilateral microphthalmia or anophthalmia. We aim to characterize these mutations in detail, test the mechanism of pathogenesis, and systematically screen a cohort of MAC patients genome-wide for related mutations. Finally, we have defined three modifiers of the mouse eyeless mutation (ey1), a recessive hypomorphic allele in the Rx homeobox gene that decreases abundance of the Rx polypeptide in the ZRDCT strain, creating a sensitized background to identify additional MAC genes in this animal model (Tucker et al. 2001). These modifier loci (ey2, ey3, ey4) are necessary for expression of the anophthalmia trait and exhibit strong pairwise interactions in an F2 cross. Positional candidate genes have been identified, including one required for morphogenesis of the ventral optic cup, and two antagonists of the Wnt signaling pathway, which is known to restrict the eye field in metazoans. We propose these modifiers enhance penetrance of the eyeless trait by increasing Wnt activity within head ectoderm. We aim to refine the mapping of ey2-ey4, and test this hypothesis using specific targeted mutations and conditional knockout mice. PUBLIC HEALTH RELEVANCE: We will find mutations that cause the eyes to be absent (anophthalmia), very small or severely malformed (coloboma) at birth. We will use genetic linkage analysis to test pedigrees with multiple affected children, and will determine the molecular basis of these disorders. We will also test specific gene interactions that produce an eyeless trait in laboratory mice. These studies explore the earliest steps in eye formation. Our results will improve diagnosis and understanding of human eye malformations, and the complex genetic factors underlying birth defects.