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Editors Selection IGR 7-2

Genetics: CCT as endophenotype for POAG

Comment by Ananth Viswanathan on:

27444 Distribution of COL8A2 and COL8A1 gene variants in Caucasian primary open angle glaucoma patients with thin central corneal thickness, Desronvil T; Logan-Wyatt D; Abdrabou W et al., Molecular Vision, 2010; 16: 2185-2191

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This study takes an interesting approach to elucidating the genetic basis of primary open-angle glaucoma (POAG). Desronvil et al. (1566) attempt to do this by studying the genetic basis of central corneal thickness (CCT). They propose CCT as an 'endophenotype' of POAG. CCT does at least partially fulfil the criteria of an endophenotype: it is associated with disease in the population, it is heritable, it is present in an individual whether or not disease is present and it co-segregates to an extent with the disease (Gottesman II, Gould TD. Am J Psychiatry 2003; 160: 636-645). The study identified mutations in the COL8A2 gene, which codes for a subunit of collagen VIII and in which mutations have been described in mice with thin corneas, in three out of eight Caucasian patients with POAG and 'thin' corneas. In none of eight patients with 'thick' corneas mutations were found.

The authors do not calculate the probability that these findings may have arisen by chance. The study also if affected by ascertainment bias: raised intraocular pressure, a known covariate of CCT, was used as part of the diagnostic criteria for POAG. This bias may have weakened the power of the study to identify mutations associated with thin corneas in POAG. Nevertheless, the findings of the study stand as interesting and point the way to further similar work, for example, as the authors suggest, in a cohort of African descent.

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