Contribution of Polygenic Scores to Progression Independent of Relapse Activity in Multiple Sclerosis

Background: Despite effective therapeutic control of relapses, many patients with multiple sclerosis (MS) experience, from the earliest phases of disease, disability accrual, which mostly occurs as progression independent of relapse activity (PIRA). In this observational study, we aimed at evaluating the genetic contribution to PIRA, using polygenic risk scores (PRS) in a cohort of 1162 Italian patients. Methods: PRS were derived from the largest multi-centric genome-wide association study on MS severity, conducted on more than 20,000 patients. The scores were computed at 5 p-value thresholds after a clumping procedure. Association with the rate of PIRA events was tested by fitting negative binomial regression models. Results: Analyses revealed a trend for association of PRS with the rate of PIRA events, which were significant in the subset of patients with age at onset ≤ 50 years (Rate Ratio = 1.148, 95% CI: 1.01 to 1.304, p = 0.0328). An interaction effect was identified between PRS and AAO, indicating a significant mild antagonistic effect (RRint = 0.98, 95% CI: 0.96 to 1.0, p = 0.033). Conclusions: Our results suggest an influence of severity-related genetic load on the rate of PIRA events, especially in subjects with disease onset before the age of 50 years, characterized by a less prominent effect of aging processes on disability accumulation. This finding supports previous observations from other studies of an age-dependent influence of genetic risk scores on complex traits.