Shiels Alan, Bennett Thomas M, Knopf Harry L S, Maraini Giovanni, Li Anren, Jiao Xiaodong, Hejtmancik J Fielding
Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA.
Mol Vis. 2008;14:2042-55. Epub 2008 Nov 12.
Cataracts are a clinically and genetically heterogeneous disorder affecting the ocular lens, and the leading cause of treatable vision loss and blindness worldwide. Here we identify a novel gene linked with a rare autosomal dominant form of childhood cataracts segregating in a four generation pedigree, and further show that this gene is likely associated with much more common forms of age-related cataracts in a case-control cohort.
Genomic DNA was prepared from blood leukocytes, and genotyping was performed by means of single nucleotide polymorphism (SNP) markers, and short tandem repeat (STR) markers. Linkage analyses were performed with the GeneHunter and MLINK programs, and association analyses were performed with the Haploview and Exemplar programs. Mutation detection was achieved by PCR amplification of exons and di-deoxy cycle-sequencing.
Genome-wide linkage analysis with SNP markers, identified a likely disease-haplotype interval on chromosome 1p (rs707455-[approximately 10 Mb]-rs477558). Linkage to chromosome 1p was confirmed using STR markers D1S2672 (LOD score [Z]=3.56, recombination distance [theta]=0), and D1S2697 (Z=2.92, theta=0). Mutation profiling of positional-candidate genes detected a heterozygous transversion (c.2842G>T) in exon 17 of the gene coding for Eph-receptor type-A2 (EPHA2) that cosegregated with the disease. This missense change was predicted to result in the non-conservative substitution of a tryptophan residue for a phylogenetically conserved glycine residue at codon 948 (p.G948W), within a conserved cytoplasmic domain of the receptor. Candidate gene association analysis further identified SNPs in the EPHA2 region of chromosome 1p that were suggestively associated with age-related cataracts (p=0.007 for cortical cataracts, and p=0.01 for cortical and/or nuclear cataracts).
These data provide the first evidence that EPHA2, which functions in the Eph-ephrin bidirectional signaling pathway of mammalian cells, plays a vital role in maintaining lens transparency.
白内障是一种影响眼晶状体的临床和遗传异质性疾病，是全球可治疗视力丧失和失明的主要原因。在此，我们在一个四代家系中鉴定出一个与罕见的常染色体显性遗传性儿童白内障相关的新基因，并进一步表明在一个病例对照队列中，该基因可能与更常见的年龄相关性白内障形式有关。
从血液白细胞中提取基因组DNA，通过单核苷酸多态性（SNP）标记和短串联重复序列（STR）标记进行基因分型。使用GeneHunter和MLINK程序进行连锁分析，使用Haploview和Exemplar程序进行关联分析。通过外显子的PCR扩增和双脱氧循环测序进行突变检测。
使用SNP标记进行全基因组连锁分析，在1号染色体p臂上确定了一个可能的疾病单倍型区间（rs707455-[约10 Mb]-rs477558）。使用STR标记D1S2672（对数优势分数[Z]=3.56，重组距离[θ]=0）和D1S2697（Z=2.92，θ=0）证实了与1号染色体p臂连锁。对定位候选基因的突变分析在编码Eph A2型受体（EPHA2）的基因第17外显子中检测到一个杂合颠换（c.2842G>T），该突变与疾病共分离。这种错义变化预计会导致在受体保守的胞质结构域内，第948密码子处一个系统发育保守的甘氨酸残基被色氨酸残基非保守取代（p.G948W）。候选基因关联分析进一步确定了1号染色体p臂上EPHA2区域的SNP，这些SNP与年龄相关性白内障有提示性关联（皮质性白内障p=0.007，皮质性和/或核性白内障p=0.01）。
这些数据首次证明，在哺乳动物细胞的Eph-ephrin双向信号通路中起作用的EPHA2在维持晶状体透明度方面起着至关重要的作用。
