This is in line with the findings of a recent study comparing the two assays in patients with multiple sclerosis [11] and may be explained by the fact that several factors that affect NfL levels in the serum, such as creatinine and cholesterol levels, do not pass the blood–CSF barrier and thus do not influence NfL levels in the CSF [42,43]. The gene discussed is NEFL; the disease is multiple sclerosis.