Neurofilament light chain (NFL), a marker of underlying axonal damage, can be reliably quantified using immunoassay in both CSF and plasma, even at low concentrations, and has been shown across several cohorts to correlate with poorer outcomes: CSF NFL is increased in PD patients with cognitive impairment185 and higher plasma NFL values predict subsequent MCI and dementia141,183,186. The gene discussed is NEFL; the disease is Parkinson disease.