Department of Ophthalmology, Peking University Third Hospital, Beijing, China.
Am J Hum Genet. 2012 Jan 13;90(1):40-8. doi: 10.1016/j.ajhg.2011.11.026. Epub 2012 Jan 5.
Ocular coloboma is a developmental defect of the eye and is due to abnormal or incomplete closure of the optic fissure. This disorder displays genetic and clinical heterogeneity. Using a positional cloning approach, we identified a mutation in the ATP-binding cassette (ABC) transporter ABCB6 in a Chinese family affected by autosomal-dominant coloboma. The Leu811Val mutation was identified in seven affected members of the family and was absent in six unaffected members from three generations. A LOD score of 3.2 at θ = 0 was calculated for the mutation identified in this family. Sequence analysis was performed on the ABCB6 exons from 116 sporadic cases of microphthalmia with coloboma (MAC), isolated coloboma, and aniridia, and an additional mutation (A57T) was identified in three patients with MAC. These two mutations were not present in the ethnically matched control populations. Immunostaining of transiently transfected, Myc-tagged ABCB6 in retinal pigment epithelial (RPE) cells showed that it localized to the endoplasmic reticulum and Golgi apparatus of RPE cells. RT-PCR of ABCB6 mRNA in human cell lines and tissue indicated that ABCB6 is expressed in the retinae and RPE cells. Using zebrafish, we show that abcb6 is expressed in the eye and CNS. Morpholino knockdown of abcb6 in zebrafish produces a phenotype characteristic of coloboma and replicates the clinical phenotype observed in our index cases. The knockdown phenotype can be corrected with coinjection of the wild-type, but not mutant, ABCB6 mRNA, suggesting that the phenotypes observed in zebrafish are due to insufficient abcb6 function. Our results demonstrate that ABCB6 mutations cause ocular coloboma.
眼组织缺损(coloboma)是一种眼部发育缺陷，是由于视裂异常或不完全闭合所致。该疾病表现出遗传和临床异质性。我们采用定位克隆方法，在中国一个常染色体显性遗传眼组织缺损的家系中发现了 ABC 转运蛋白 ABCB6 的一个突变。该家系的 7 位受影响成员存在 Leu811Val 突变，而 3 代中的 6 位未受影响成员则不存在该突变。对该家系中发现的突变进行连锁分析，θ=0 时的 LOD 得分为 3.2。对 116 例散发的小眼伴虹膜缺损（MAC）、单纯性虹膜缺损和无虹膜患者的 ABCB6 外显子进行了序列分析，在 3 例 MAC 患者中发现了另一个突变（A57T）。这两个突变均不存在于匹配的对照人群中。在视网膜色素上皮（RPE）细胞中转染瞬时表达的 Myc 标记的 ABCB6 后进行免疫染色，结果显示其定位于 RPE 细胞的内质网和高尔基体。在人细胞系和组织中进行的 ABCB6 mRNA 的 RT-PCR 分析表明，ABCB6 在视网膜和 RPE 细胞中表达。利用斑马鱼，我们发现 abcb6 在眼睛和中枢神经系统中表达。在斑马鱼中用 abcb6 的 morpholino 敲低，可产生具有 coloboma 特征的表型，并且复制了我们家系中索引病例观察到的临床表型。用野生型 abcb6 mRNA 而非突变型 abcb6 mRNA 进行共注射，可纠正该敲低表型，表明在斑马鱼中观察到的表型是由于 abcb6 功能不足所致。我们的研究结果表明 ABCB6 突变可导致眼组织缺损。
