New genetic risk factors for multiple sclerosis found
Genes point to the importance of immune system proteins.
People with one of two common gene variants may be at increased risk of developing the autoimmune disorder multiple sclerosis (MS), researchers say.
Both variants encode components of the immune system that are involved in preventing the body from attacking its own cells.
Two papers1,2 published today in Nature Genetics independently pinpoint one of the variants, in the 'interleukin-7 receptor alpha chain' (IL7R) gene. A third research team scanned the full genome for variants associated with MS, and found both IL7R and another interleukin receptor gene — 'interleukin-2 receptor alpha' (IL2R) — among the top hits3.
In MS the body's immune system attacks the insulating sheath that surrounds and protects neurons, leading loss of motor function and cognitive decline. Interleukin-2 and interleukin-7 are immune system proteins that play a role in the function of regulatory T-cells, which help suppress autoimmunity.
Direction for development
The three research teams analyzed thousands of patients of European descent, and found that a single base pair difference in the IL7R gene increased the risk of having MS by about 20%. That risk is too low to make IL7R useful for a genetic test, cautions Margaret Pericak-Vance, a geneticist at the University of Miami in Florida, and an author on one of the studies. "A lot of people carry this particular variant, and they don't get multiple sclerosis," she says. Roughly 70% of the European population is likely to have the variant.
Nevertheless, the findings do provide a better understanding of the disease, and suggest a direction for developing new therapeutic approaches, says George Ebers, an Oxford University neurologist who was not involved in the studies. "It's a small effect to be sure," he says. "But, it's conceptually important because it gives some indication as to what the basic underlying processes in multiple sclerosis might be."
Risk of developing MS varies widely according to ethnicity, gender, and even geographic location, suggesting a complex interplay between genetic and environmental factors. A link had previously been shown between risk of MS and variations in a set of genes called major histocompatibility complex genes, which encode proteins that help the immune system distinguish between self and non-self. But that link was found 30 years ago, and no other firm genetic connections had been made since then.
David Hafler, an immunologist at Harvard Medical School, in Massachusetts, notes that variants in IL7R and IL2R are also associated with increased risk of type I diabetes. This could imply a causal link between the two autoimmune diseases, he says, possibly due to the role that the two interleukins play in the regulatory T-cell function.
- Gregory, S. G. et al. Nat. Genet. doi:0.1038/ng2103 (2007).
- Lundmark, F. et al. Nat. Genet. doi: 10.1038/ng2106 (2007).
- Hafler, D. A., et al. N. Engl. J. Med. doi: 10.1056/NEJMoa073493 (2007).