One such study analyzed serum NfL at baseline and at six-month follow-up using the Simoa NF-Light kit in neurologically healthy controls, untreated relapsing multiple sclerosis, and secondary and primary progressive multiple sclerosis.42 Elevation of NfL in healthy controls was positively associated with increased age, and at follow-up, NfL was elevated compared with baseline. The gene discussed is NEFL; the disease is primary progressive multiple sclerosis.