NEFL and multiple sclerosis: ,30,46, 47, 48 In particular, a study of patients with multiple sclerosis showed an inverse correlation between PAG, p-cresyl sulfate, and indoxyl sulfate levels and MRI measurements of the cortical volume; the latter is directly correlated with the level of neurofilament light chain in the cerebrospinal fluid and thus serves as a well-established biomarker of neurodegeneration.48