ROCHESTER, Minn. — Mayo Clinic researchers have validated a new antibody test to diagnose multiple sclerosis (MS), a potentially disabling disease of the brain and spinal cord. Nearly 1 million people in the U.S. are affected by MS, according to the National Multiple Sclerosis Society. An antibody typically consists of two immunoglobulin heavy chains and two light chains. There are two types of light chains: kappa and lambda. The validated test measures kappa immunoglobulin free…