Washington, Nov 23: Scientists at the Yale School of Medicine have identified a gene variant that increases the risk of developing the aggressive "wet" form of age-related macular degeneration (AMD), the most common cause of blindness in people over 50 years of age.

Last year, Josephine Hoh, senior author on one of the two studies, had identified a gene for dry AMD, and found that both wet and dry AMD are associated with a variant in the complement factor H (CFH) gene on chromosome 1.

She now claims to having found a single nucleotide polymorphism (SNP), a one-base change in the sequence, of the regulatory part of the HTRA1 gene on chromosome 10, which leads to greatly increased risk of developing the wet form of AMD.

The study demonstrates that two major genes, CFH and HTRA1, affect the risk for a distinct component of the AMD phenotype.

Hoh and her colleagues, Michael Snyder and Colin Barnstable, did trans-racial gene mapping by comparing genomes between precisely defined populations to find the incidence of SNP in a Chinese population, which included 96 participants with AMD and 130 with normal vision.

"We found that patients with the HTRA1 SNP were 10 times more likely to have wet AMD than those without this gene variant. While this is only preliminary work, it points to possible directions for future treatment of wet AMD," said Hoh.

Hoh also worked on a replication study led by Kang Zhang at the University of Utah School of Medicine, which found a link between the same SNP and AMD.

To confirm the association, the Utah team also examined several donor eyes, and measured the expression of the gene and the encoded protein. They found that the expressions were elevated in the eyes of patients who carry HTRA1.

"The marker we have identified is very much associated with AMD, but no one has ever pinpointed the clinical features of the gene. We need to conduct further analysis in order to understand the biological mechanisms," said Hoh.

The findings have been reported in two articles published in the journal Science. (ANI)