LRP2 gene were linked with a greater relapse risk. To identify additional genetic risk factors, researchers at KU Leuven in Belgium and colleagues conducted a genome-wide association study (GWAS) involving 506 MS patients, who had a median duration of disease of four years. A GWAS looks for genetic variants that might serve as markers predicting the presence of a certain trait — in this case, a greater rate of relapses. Relapse was defined according to patient-reported symptoms or signs of acute inflammation due to loss of myelin in the central nervous system — a hallmark of MS — lasting for at least 24 hours, in the absence of fever or infection.