The aim of this cross-sectional study was to examine the associations between neurodegenerative biomarkers—specifically plasma neurofilament light chain (pNfL) levels and MRI-derived brain volume measurements—and clinical outcomes, including cognitive performance and physical disability, in patients with early-stage relapsing–remitting multiple sclerosis (RRMS) at a young age. This evidence concerns the gene NEFL and relapsing-remitting multiple sclerosis.