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Editors Selection IGR 8-4

Genetics: eNOS Gene

Comment by Subhabrata Chakrabarti on:

28126 Association of genetic polymorphisms of eNOS with glaucoma, Liao Q; Wang D-H; Sun H-J, Molecular Vision, 2011; 17: 153-158

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Single nucleotide polymorphisms (SNPs) in the human genome have ushered in a new era of understanding the genetic basis of complex disorders including glaucoma. Eventually, they have become the choice of genetic markers in robust technologies such as genome wide association studies (GWAS) in mapping disease susceptibility gene(s). Alternatively, a relatively less robust approach using candidate SNPs in genes that are functionally implicated in glaucoma has been undertaken in several studies. Liao et al. (59) in the present study did a similar exercise on the endothelial nitric oxide synthase (eNOS) gene that was earlier characterized based on its expression profile in the glaucomatous tissues. Five tagging SNPs in eNOS were genotyped in a cohort comprising primary open-angle and primary closed-angle glaucoma cases and unaffected controls from China. No significant association was observed across these SNPs, but a weak association was seen with a haplotype tagged by 2 SNPs.

Genetic association studies should be taken with a pinch of salt as several confounders including (and not limited to) study design, phenotyping, population structure, genotyping quality, power of the study, appropriate validations and improper replications could lead to spurious and inconsistent results. Although the hypothesis is well defined, an underpowered study such as this one is unlikely to yield any meaningful results. Moreover, the specifics of two phenotype categories and further validation of the genotype data are unavailable. Hence, the reliability of the dataset is a major issue. Concurrently, the weak association of the haplotype through 2 SNPs that are neither associated nor in linkage disequilibrium indicates a false positive involvement that may be unlinked to the disease. A comprehensive analysis of the entire eNOS gene would have helped to understand the extent of its involvement in glaucoma. We will have to wait until such extensive data are available from different populations.

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