Glaucoma is the second leading cause of blindness and is estimated to affect over 66 million people worldwide. This group of diseases is typically caused by increased pressure in the eye, which slowly damages the optic nerve and leads to gradual vision loss and eventual, incurable blindness if left untreated.
The most common form of glaucoma is primary open-angle glaucoma, or POAG. Prevalence of POAG among Caucasians is approximately 1-2%, but those with African ancestry develop glaucoma at rates five times higher, and are four times more likely to become blind once they have the disease. Family history and advanced age, in addition to high intraocular pressure, are known risk factors. Studies of families and monozygotic twins suggest a genetic basis, though the specific genes involved in the majority of disease cases have remained elusive.
To explore the genetic underpinnings of POAG in individuals of African descent, a group of researchers led by Xiaodong Jiao from the National Eye Institute in Bethesda and Kang Zhang from the University of California – San Diego recently partnered with the Ministry of Health in Barbados, West Indies to search for genetic variants associated with POAG in an Afro-Caribbean population with high rates of glaucoma. In their paper, published online this week in the Proceedings of the National Academy of Sciences, they report results from a region of the genome, chromosome 2p16, that previous studies have linked to the disease. When they analyzed SNPs in this region of the genome for the Barbados study group, they found two common variants significantly associated with glaucoma.
Although the case-control study population was fairly small – about 252 individuals total with glaucoma and 130 controls – the effects of the two SNPs were large when individuals had two copies of the high-risk version. Individuals with a T at both copies of rs1533428 had about 7 times higher odds of glaucoma, while individuals with a T at both copies of rs12994401 had almost 35 times higher odds.
The authors note that while their analysis of the 2p16 region suggests multiple genetic bases for POAG in Afro-Caribbeans, this region overlaps with one that was shown to contribute unequivocally to POAG in some families. They posit that the severity of the mutations caused by different variants in this genomic area may influence whether resulting POAG is due to a single gene, or the combined effects of many genes acting together to increase risk.
Further studies are needed to confirm the associations of rs1533428 and rs12994401 with POAG in larger populations, and to identify the genes directly involved in development of glaucoma.
(SNPwatch gives you the latest news about research linking various traits and conditions to individual genetic variations. These studies are exciting because they offer a glimpse into how genetics may affect our bodies and health; but in most cases, more work is needed before this research can provide information of value to individuals. For that reason it is important to remember that like all information we provide, the studies we describe in SNPwatch are for research and educational purposes only. SNPwatch is not intended to be a substitute for professional medical advice; you should always seek the advice of your physician or other appropriate healthcare professional with any questions you may have regarding diagnosis, cure, treatment or prevention of any disease or other medical condition.)
Credit: National Eye Institute, National Institutes of Health