Genetic Basis of Congenital Anophthalmia

描述（由申请方提供）：无眼症、小眼症和缺损（MAC）是指眼睛缺失或非常小，或在视杯发育期间脉络膜裂未能闭合的出生缺陷。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，往往减少染色体畸变。已经鉴定了少数基因的突变，包括转录因子PAX 6、CHX 10、RX、SOX 2和OTX 2，以及生长因子GDF 6和BMP 4。这些在发育的关键早期阶段表达，此时眼域建立并且视原基扩展。然而，大多数案件仍然无法解释。我们已经确定了一个新的常染色体显性MAC位点的连锁分析在一个大的家系。我们的目标是完善地图的位置，并确定非重组区域内的致病突变。我们还在患有严重双侧小眼症或无眼症的儿童中发现了PAX 6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，并系统地筛选一组MAC患者的全基因组相关突变。最后，我们定义了小鼠无眼突变（ey 1）的三种修饰因子，这是Rx同源异型盒基因中的一种隐性亚型等位基因，可降低ZRDCT品系中Rx多肽的丰度，从而产生一种致敏背景，以在该动物模型中鉴定其他MAC基因（Tucker et al. 2001）。这些修饰基因座（ey 2、ey 3、ey 4）对于无眼性状的表达是必需的，并且在F2杂交中表现出强的成对相互作用。已经确定了位置候选基因，包括腹侧视杯的形态发生所需的一个，和Wnt信号通路的两个拮抗剂，这是已知的限制在后生动物的视野。我们建议这些修饰剂通过增加头部外胚层内的Wnt活性来增强无眼性状的表达。我们的目标是完善ey 2-ey 4的定位，并使用特定的靶向突变和条件性基因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（缺损）的突变。我们将使用遗传连锁分析来检测多个受影响儿童的家系，并确定这些疾病的分子基础。我们还将在实验室小鼠中测试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类眼睛畸形的诊断和理解，以及出生缺陷背后的复杂遗传因素。

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.