The association between SF and NfL noted is consistent with a previous study that explored this particular cognitive subdomain.32 A deficit in this test is a reflection of fronto-temporal dysfunction.33 Abnormalities in axonal tracts in these regions have been noted in the early stages of PD and seem to correlate with CSF NfL levels.17 This finding potentially highlights the value of more detailed neuropsychological testing, but this is of course more labour intensive than a simple blood test. The gene discussed is NEFL; the disease is Parkinson disease.