DNA and You

Is It Heritable? Twin Study Evidence Suggests Eyeball (aka Intraocular) Pressure is Substantially Affected by Genetics

As I've previously mentioned, twin studies allow an estimation of the heritability of a trait by comparing the degree of concordance in a given phenotype between MZ (identical) twins and DZ (fraternal) twins.

I recently came across a fascinating study looking at the heritability of intraocular pressure - that is -the pressure on the inside of the eyeball that ophthalmologists and optometrists measure when screening for glaucoma.  Carbonaro and colleagues, from the Twin Research and Genetic Epidemiology Unit at King's College London School of Medicine, performed a classical twin study to estimate intraocular pressure (IOP) heritability¹.  Although there was some modest variability in the heritability estimates depending on which of 3 instruments was utilized to measure IOP, the results suggested that genetic factors explain about 62 percent of the variation in IOP, with individual environmental factors and/or stochastic factors accounting for the remainder.

62 percent is impressively high, but of course does not tell us anything about the genetic architecture of the trait.  Although some progress has been made in understanding the genetics of congenital glaucoma, we have much further to go with adult glaucoma/IOP elevation.  Despite the existence of a few clues^2-4, much work remains to be done. 

Photo: By ninjapoodles via Creative Commons.

Cited References

1. Carbonaro F, Andrew T, Mackey DA, Spector TD, Hammond CJ.  Heritability of intraocular pressure: a classical twin study.  Br J Ophthalmol 92:1125-8, 2008.

2. Duggal P et al.  Identification of novel genetic loci for intraocular pressure: a genomewide scan of the Beaver Dam Eye Study.  Arch Ophthalmol 125:74-9, 2007.

3. Wiggs JL et al.  Genome-wide scan for adult onset primary open angle glaucoma.  Hum Mol Genet 9:1109-17, 2000.

4. Nemesure B et al.  A genome-wide scan for primary open-angle glaucoma (POAG): the Barbados Family Study of Open-Angle Glaucoma.  Hum Genet 112:600-9, 2003.

Is it heritable? Twin study evidence suggests acne can be inherited

Have you ever wondered whether acne risk can be inherited?  Twin studies can shed light on this question.

In a previous post, I discussed twin studies which are the genetic gold standard to determine whether the liklihood of developing a given medical condition (or trait) is subject to heritable (i.e., genetic) influences.  The concept is fairly simple: Identical twins share essentially 100% of their genetic material while fraternal twins share 50%.  If genetics plays a strong role in risk for a disease, when twin pairs in which one member has the disease are studied, both twins will have the same disease in a larger percentage of the identical twin pairs as compared to the fraternal twin pairs. 

One study applied this concept to the study of acne.  The results were clear: in this study, approximately 80% of the degree to which acne severity varied was due to genetic effects. 

Although the underlying causative genes are not known, the fact that genetics plays such a large role in the development of acne suggests that future efforts to find the underlying genes are likely to reveal new drug targets.