Identification of a novel, putative cataract-causing allele inCRYAA (G98R) in an Indian family

[摘要] Purpose: The aim of the present study was to investigate themolecular basis underlying a nonsyndromic presenile autosomal dominantcataract in a three-generation pedigree. The phenotype was progressivefrom a peripheral ring-like opacity to a total cataract with advancingage from teenage to adulthood. The visual impairment started as problemin distant vision at the age of 16 years, to diminishing vision by theage of 24.Methods: Clinical interventions included complete ophthalmologicalexamination, a collection of case history, and pedigree details. Bloodsamples were collected from available family members irrespective oftheir clinical status. A functional candidate gene approach was employedfor PCR screening and sequencing of the exons and their flanking regionsof CRYGC, CRYGD, and CRYAA genes. For structuralconsequences of the mutated αA-crystallin we used thebioinformatics tool of the ExPASy server.Results: Sequence analysis of CRYGC and CRYGD genes excludedpossible causative mutations but identified known polymorphisms.Sequencing of the exons of the CRYAA gene identified a sequencevariation in exon 2 (292 G->A) with a substitution of Gly to Arg atposition 98. All three affected members revealed this change but it wasnot observed in the unaffected father or sister. The putative mutationobliterated a restriction site for the enzyme BstDSI. The same waschecked in controls representing the general population of the sameethnicity (n=30) and of randomly selected DNA samples fromophthalmologically normal individuals from the population-based KORA S4study (n=96). Moreover, the Gly at position 98 is highly conservedthroughout the animal kingdom. For the mutant protein, the isoelectricpoint was raised from pH 5.77 to 5.96. Moreover, an extendedα-helical structure is predicted in this region.Conclusions: The G98R mutation segregates only in affected familymembers and is not seen in representative controls. It represents verylikely the fourth dominant cataract-causing allele in CRYAA. In allreported alleles the basic amino acid Arg is involved, suggesting themajor importance of the net charge of the αA-crystallin forfunctional integrity in the lens.

[学科分类] 生物化学/生物物理