Multiple sclerosis symptoms can be affected by a pair of "angel and devil" genes that fight to make a patient healthy or ill, Oxford University researchers have found.

The discovery could help scientists find new ways of tackling the potentially-devastating disease suffered by about 85,000 people in the UK. And it has has been welcomed by the Multiple Sclerosis Society as a step towards new treatments for the condition.

One of the genes thought to be responsible for MS is called DR2b.

Scientists have learned that it is the "evil twin" of a pair of DR2 genes. While DR2b works to increase the rogue immune response that causes symptoms of MS, its partner gene DR2a tries to prevent the damage.

Thanks to DR2a, MS symptoms, which can range from numbness to paralysis, are dampened.

Researchers believe this could be why some patients are worse affected by the disease than others. Prof Lars Fugger, of the Medical Research Council's human immunology unit at Oxford University, led the work on the study.

He said: "Multiple sclerosis is caused by the immune system attacking the body.

"The DR2b gene clearly tells the immune system to go hard into battle against the body's own tissue, so it starts to work in a way that actually damages the person.

"For this reason, natural selection has eliminated the gene on its own, but allowed it to be inherited only when it is accompanied by another gene (DR2a) which tempers its effect."

MS is a lifelong condition with a wide variety of symptoms, including pain, muscle problems, impaired mental function, and poor vision. In severe cases it can lead to disabling loss of limb movement.

Prof Fugger's team bred mice with different combinations of DR2 genes in order to investigate their effects on the body.

Mice engineered to carry only DR2b had a severe form of the disease which is only seen in a minority of human patients.

Those with both genes were less likely to develop MS in the first place or had a less severe form of the disease.

In some cases, mice which were carrying the "good" gene spontaneously recovered.

Beverley Hughes, 46, from Witney, the welfare officer of the MS Society's Oxford and District branch, said: "Whenever new research comes out, we always hope it encourage money to support MS charities and to help fund research into multiple sclerosis."

Simon Gillespie, chief executive of the MS Society, said: "We share the researchers' hope that it could eventually play a part in helping to treat this very variable and unpredictable condition."