Schiaffino M V, Bassi M T, Rugarli E I, Renieri A, Galli L, Ballabio A
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA.
Hum Mol Genet. 1995 Mar;4(3):373-82. doi: 10.1093/hmg/4.3.373.
Ocular albinism type 1 (OA1) is an X-linked recessive disorder characterized by a major impairment of visual acuity, nystagmus, strabismus, photophobia and retinal hypopigmentation. From the analysis of patients carrying deletions and translocations involving the distal short arm of the X chromosome (Xp22.3) we have identified a region of approximately 110 kb in which the OA1 gene must lie. We have extensively searched for genes in this region using a variety of techniques which included exon amplification, cDNA selection and direct hybridization of cosmid inserts to cDNA libraries. Putative exons identified by exon amplification were used to screen a human retina cDNA library and several cDNA clones corresponding to an approximately 7.5 kb transcript were isolated and characterized. Transcripts of this newly identified gene were found to be abundant in retina and melanoma and could also be detected in brain, placenta, lung, kidney and pancreas. Interestingly, sequence analysis revealed that this new gene encodes a 1616 amino acid protein sharing significant similarities with the Apical Protein from Xenopus laevis (APX) which is implicated in amiloride-sensitive sodium channel activity. The gene, termed APXL (APX-Like), spans approximately 160 kb, contains 10 exons and covers over 70% of the 110 kb critical region for OA1. A truncated pseudogene sharing very high levels of homology with the rat eIF-5 gene, a eukaryotic translation initiation factor, was found to lie in the middle of intron 1. APXL was found deleted in two patients with contiguous gene syndromes including OA1 and in one patient with isolated OA1. Mapping, expression and patient analysis data led us to consider the APXL gene a strong candidate for the OA1 gene. DNA from 57 unrelated patients with OA1 was, therefore, scanned for mutations in the coding region, using both SSCP analysis and direct sequencing. No functionally significant mutation was identified, suggesting that APXL is not directly involved in OA1. Further studies are needed to clarify the physiologic role of this highly conserved gene.
1型眼白化病（OA1）是一种X连锁隐性疾病，其特征为视力严重受损、眼球震颤、斜视、畏光和视网膜色素减退。通过对携带涉及X染色体短臂远端（Xp22.3）缺失和易位的患者进行分析，我们确定了一个约110 kb的区域，OA1基因必定位于该区域内。我们使用了多种技术在该区域广泛搜索基因，这些技术包括外显子扩增、cDNA筛选以及黏粒插入片段与cDNA文库的直接杂交。通过外显子扩增鉴定出的推定外显子用于筛选人视网膜cDNA文库，并分离和鉴定了几个与约7.5 kb转录本相对应的cDNA克隆。发现这个新鉴定基因的转录本在视网膜和黑色素瘤中大量存在，在脑、胎盘、肺、肾和胰腺中也能检测到。有趣的是，序列分析表明这个新基因编码一种1616个氨基酸的蛋白质，与非洲爪蟾的顶端蛋白（APX）有显著相似性，APX与氨氯地平敏感的钠通道活性有关。该基因被命名为APXL（类APX），跨度约160 kb，包含10个外显子，覆盖了OA1关键区域110 kb的70%以上。发现一个与大鼠eIF-5基因（一种真核翻译起始因子）具有高度同源性的截短假基因位于内含子1中间。在两名患有包括OA1在内的连续基因综合征的患者和一名患有孤立性OA1的患者中发现APXL缺失。定位、表达和患者分析数据使我们认为APXL基因是OA1基因的有力候选者。因此，我们使用单链构象多态性分析（SSCP）和直接测序对57名无关的OA1患者的DNA进行编码区突变扫描。未发现功能上有意义的突变，这表明APXL不直接参与OA1的发病机制。需要进一步研究来阐明这个高度保守基因的生理作用。
