Pauli Silke, Söker Torben, Klopp Norman, Illig Thomas, Engel Wolfgang, Graw Jochen
Institute of Human Genetics, University of Göttingen, Göttingen, Germany.
Mol Vis. 2007 Jun 19;13:962-7.
The study demonstrates the functional candidate gene analysis in a cataract family of German descent.
We screened a German family, clinically documented to have congenital cataracts, for mutation in the candidate genes CRYG (A to D) and CRYBB2 through polymerase chain reaction analyses and sequencing.
Congenital cataract was first observed in a daughter of healthy parents. Her two children (a boy and a girl) also suffer from congenital cataracts and have been operated within the first weeks of birth. Morphologically, the cataract is characterized as nuclear with an additional ring-shaped cortical opacity. Molecular analysis revealed no causative mutation in any of the CRYG genes. However, sequencing of the exons of the CRYBB2 gene identified a sequence variation in exon 5 (383 A>T) with a substitution of Asp to Val at position 128. All three affected family members revealed this change but it was not observed in any of the unaffected persons of the family. The putative mutation creates a restriction site for the enzyme TaiI. This mutation was checked for in controls of randomly selected DNA samples from ophthalmologically normal individuals from the population-based KORA S4 study (n=96) and no mutation was observed. Moreover, the Asp at position 128 is within a stretch of 12 amino acids, which are highly conserved throughout the animal kingdom. For the mutant protein, the isoelectric point is raised from pH 6.50 to 6.75. Additionally, the random coil structure of the protein between the amino acids 126-139 is interrupted by a short extended strand structure. In addition, this region becomes hydrophobic (from neutral to +1) and the electrostatic potential in the region surrounding the exchanged amino acid alters from a mainly negative potential to an enlarged positive potential.
The D128V mutation segregates only in affected family members and is not seen in representative controls. It represents the first mutation outside exon 6 of the human CRYBB2 gene.
本研究展示了对一个德裔白内障家族进行功能候选基因分析的过程。
我们对一个临床上被诊断为患有先天性白内障的德裔家族进行筛查，通过聚合酶链反应分析和测序来检测候选基因CRYG（A至D）和CRYBB2中的突变。
先天性白内障首次在健康父母的一个女儿身上被观察到。她的两个孩子（一个男孩和一个女孩）也患有先天性白内障，并在出生后的第一周内接受了手术。从形态学上看，白内障的特征为核性白内障，并伴有额外的环形皮质混浊。分子分析显示，在任何一个CRYG基因中均未发现致病突变。然而，对CRYBB2基因外显子的测序发现外显子5（383 A>T）存在序列变异，导致第128位的天冬氨酸被缬氨酸取代。所有三名受影响的家庭成员均显示出这种变化，但在该家族的任何未受影响的个体中均未观察到。该推定突变产生了一个TaiI酶的限制性位点。在基于人群的KORA S4研究中随机选择的眼科正常个体的DNA样本对照（n = 96）中检查了该突变，未观察到突变。此外，第128位的天冬氨酸位于一段12个氨基酸的区域内，该区域在整个动物界中高度保守。对于突变蛋白，其等电点从pH 6.50升高到6.75。此外，蛋白质在氨基酸126 - 139之间的无规卷曲结构被一个短的延伸链结构打断。另外，该区域变得疏水（从中性变为 +1），并且在交换氨基酸周围区域的静电势从主要为负电位变为增大的正电位。
D128V突变仅在受影响的家庭成员中分离，在代表性对照中未观察到。它代表了人类CRYBB2基因外显子6之外的首个突变。
