A large study of European populations has uncovered seven new clusters of defective genes that may be responsible for rheumatoid arthritis, a painful and disabling disease that affects mainly the joints.

The paper was published in Nature Genetics on Monday together with findings of a separate study in Japan, which identified one of the seven genetic clusters as possibly causing the chronic inflammatory disease among Japanese.

“The findings leverage us to better understand the basic biology of rheumatoid arthritis (RA), with the goals of developing new targets for therapy and new biomarkers for diagnosis and prognosis,” wrote research scientist Eli Ayumi Stahl at the Brigham and Women’s Hospital in Boston in the United States, who led the study on European populations.

The study was also intended “to develop better genetic tests for RA risk, especially in people already at risk (such as arthritis patients or relatives of patients with autoimmune disorders),” Stahl told Reuters.

RA affects about 1 percent of the world’s population. Apart from the joints, it may affect the skin, heart, lungs, kidneys and blood vessels. Many end up with deformed hands and feet, resulting in loss of functions and movement.

In the European study, Stahl and colleagues repeated six previous studies involving 5,539 patients, analyzing their genes using the latest technology. They shortlisted 34 genetic variants which they considered most suspect in causing RA.

They then checked if those genetic defects were found in another batch of 6,768 RA patients in Canada, North America, the Netherlands and Britain. Ten of the 34 variants figured most prominently in this replication phase.

“Ten of the 34 variants tested were validated in the replication phase of our study. Three were previously implicated in RA, leaving the 7 new ones mentioned above,” Stahl wrote.

“This is more RA risk variants discovered in a single study than any other study to date, underscoring the importance of large-scale studies and the collaborations that enable them in order to make progress in unraveling common, complex diseases.”

“Our results further suggest that many more RA risk variants remain to be definitively identified,” Stahl added.

In the Japanese study, researchers led by Yuta Kochi at the RIKEN Center for Genomic Medicine in Yokohama, Japan, analyzed genes of 7,039 RA patients and identified a common genetic mutant near the CCR6 gene.

The CCR6 gene was also identified in the European study.

SOURCE: Nature Genetics, online May 10, 2010.