http://www.businessweek.com/news/201...-update1-.html

Biogen Seeks Test for Brain Disease Linked to MS Drug (Update1)

Thought this paragraph was interesting

“Biogen is looking at other biological signs of PML risk that may be incorporated to improve the test, Sandrock said. In those who test positive, Biogen is testing for markers to further determine which patients are at high risk, Sandrock said. Those markers may include certain genes that increase the risk of a brain infection, or viral mutation that allows JC virus to live in brain tissue.”