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Genetics may play role in CCT
Invest Ophthalmol Vis Sci. 2008;49:4303-4307.
Genetics may play a key role in determining central corneal thickness, a risk factor for adult-onset primary open-angle glaucoma.
A population-based study included 449 twin pairs recruited from southern China. Subject age ranged from 8 years to 16 years with a mean of 11.8 years. Researchers used the Pentacam non-contact tonometer (Oculus) to obtain objective pachymetry measurements.
Data showed heritability of CCT to be higher in girls (0.91) than in boys (0.88). No statistically significant difference was seen in CCT between identical twins (551.9 µm) and fraternal twins (551.7 µm).
CCT twin correlations were 0.90 for monozygotic boys, 0.92 for monozygotic girls, 0.56 for dizygotic boys, 0.61 for dizygotic girls and 0.44 for opposite-sex dizygotic twins.
“There is not a simple explanation of the genetic effect of CCT, given that its biological determinants remain unknown,” the study authors said. “No specific genes or chromosomal regions have been reported to be linked to CCT.”
It is of some interest, confirming the heretofore limited work of Toh, and colleagues, on the subject of heritability of CCT in twins. Interesting as it may be from a genetic viewpoint, as the study subjects were of child to adolescent age, it was not feasible to verify the important clinical correlate as to the development of open-angle glaucoma among the same cohort. However, as the concordance of measurements, especially among monozygotic twin pairs was very tight, it would be expected that as CCT is a major risk factor for OAG, the at-risk pairs would ultimately both be likely to develop the clinical disease.
Apart from the science, however, there is really no profound clinical practice implication apart from the obvious: OAG in one member of a twin pair renders the other twin to be almost certain to have the disease as well. As to future research implications, the genetic analysis of both monozygotic and dizygotic twins for specific OAG genes may be of interest as of course would long-term (50-year) follow-up of the current study population to ascertain which pairs actually develop OAG and whether this would also correlate, as predicted, with their CCT values.
– Kenneth R. Kenyon, MD
OSN Cornea/External Disease Editor Emeritus, Boston, Mass.