A number of studies have found significant increases in CSF NfL levels over time in patients with PSP studied serially.45-48 Bäckström et al.47 found that in PSP subjects with a short disease duration (13 months median) CSF NfL increased by 27.1% over 12 months, while it remained unchanged in PD and multiple system atrophy subjects. This evidence concerns the gene NEFL and Parkinson disease.