NEFL and multiple sclerosis: In patients with HIV, elevated levels of CSF NfL have been shown to correlate with decreased NAA/Cre in multiple brain regions, indicating compromised neuronal health and stability.41 In multiple sclerosis patients, the same inverse relationship has been observed between serum NfL and NAA/Cre at baseline, yet is not present at 12 and 36 months following haematopoietic stem cell transplantation.42 Given the elevated concentration of NfL in Huntington’s disease, we hypothesized that an inverse relationship with tNAA and tCre would be present in the putamen of Huntington’s disease patients.