A new study may provide some clues about why multiple sclerosis is more common in women, after researchers were able to pinpoint a difference in the brains of women that may cause the discrepancy in diagnoses.

Little is known about what causes MS in general and why women are a greater risk for the disabling disease, which affects the central nervous system and is characterized by initial symptoms like vision problems and leads to muscle weakness and coordination and balance difficulty. MS can cause numbness, pain, speech problems, dizziness and hearing loss, as well as cognitive issues like memory loss or difficulty concentrating. In the most devastating cases, MS can lead to paralysis. And it's as much as four times more common in women than in men.

The research, conducted at Washington University School of Medicine in St. Louis and published in the Journal of Clinical Investigation, found higher levels of a blood vessel receptor protein called S1PR2 in both female mice and women who were vulnerable to MS. What's more, S1PR2 was even higher in the parts of the brains of the women and mice that MS usually affects.

"It was a 'Bingo!' moment –- our genetic studies led us right to this receptor," senior author and associate professor of medicine at Robyn Klein, M.D., Ph.D., said in a statement. "When we looked at its function in mice, we found that it can determine whether immune cells cross blood vessels into the brain. These cells cause the inflammation that leads to MS."

Among the female mice, Klein and her team found 20 genes in areas of the brain typically affected by MS that were active at different levels than in male mice. Previous research had identified S1PR2 as a protein that dictates the ease with which cells and molecules pass through the walls of blood vessels. In the new research, S1PR2 was found to also regulate which cells cross from the blood vessels into the brain, which could allow the inflammatory cells that lead to MS to enter the central nervous system, according to the press release.

The highest levels of S1PR2 in human brain tissue samples were in two female MS patients who had "relapsing and remitting MS", meaning their symptoms flared irregularly.