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B. L. Sukka Ganesh, Sr., T. R. R. B. Sukka Ganesh, Sr., Molecular Genetics-Age-Related-Cataract; Age Related Cataracts-Associated With Mutation 14CT in Exon-6 of CRYBB2 Gene. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4426.
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The present study is an attempt made to screen different types of age-related cataract for the CRYBB2 exon-6 mutation (C → T transition) that is found to be causally related with congenital Coppock like cataract.
Genomic DNA samples were digested with 3 units of Dde-I enzyme and amplified by ARMS PCR, electrophoresed on 1% agarose gel stained with ethidium bromide and genotyped after visualizing under UV. The presence of single band of 400bp fragment was typed as DdeI +/+, 220 bp fragment as DdeI -/- and 400bp +220bp fragments as DdeI +/-.
Of 275 age-related cataract patients studied, 96 were diagnosed as Nuclear (NC), 49 as Cortical (CC), 45 as Posterior Subcapsular (PSC), and 85 as Mixed type MT. The incidence of females was high in NC (57.3%) and MT (64.7%). The ages at onset were 60.0±9.8 in NC; 55.2±11.2 in CC ; 51.2±12.9 I PSC; 55.9±9.9 in MT. The patients were divided into presenile and senile groups (with onset <50 and >51 years). Presenile cases were higher in CC (26.5%) and PSC (40.0%) as compared to NC (6.3%) cases. Only males were reported to be smokers with high frequencies in NC (53.7%) CC (66.7%) PSC (63.6%) cases as compared to non-smokers and controls (37.3%). Positive family were reported to be high in CC (16.3%) as compared to others cataracts.All the controls showed normal genotype for C→T transition while in patients heterozygotes were also detected. None of the patients and controls had homozygous mutation. The heterozygote was higher in CC (24.5%) followed by PSC (17.8%), NC (5.2%) and MT (4.7%). The frequency of heterozygotes were more in the female patients (NC-9.1%; CC-44.0%; PSC-21.7%) as compared to males (Nc-0; CC-4.2%; PSC-13.6%). Smoker with CC (Χ2- 3.92 P<0.025) and PSC (Χ2-6.84 P<0.025), showed significantly high risk for developing lens opacity. Compared to controls the genotypic distribution differed in different types of cataracts (NC-7.88 p<7.88; CC-34.8 p<0.001; PSC-25.6 p<0.001; MT-7.38 p<0.01) indicating high risk for cataract development in carriers for mutation. The comparison of allelic frequencies showed significant deviation from controls in cases of CC (Χ2- 14.6 P<0.001) and PSC (Χ2- 10.3, P<0.01) and also when all the cataracts were pooled (Χ2- 5.81, P<0.025).
The present results may reflect the possibility of a) Common gene based etiology for congenital and senile cataracts, b) Presence of modifier factors influencing the phenotype caused by same mutation in different subjects
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