NEFL and Parkinson disease: In PD patients, CSF NfL has been shown to be higher in patients with worse motor function and cognitive impairment, even if the baseline concentration of NfL does not seem to predict conversion to dementia in cognitively intact PD patients20, and studies have demonstrated that high CSF NfL in early PD predicts subsequent conversion to PDD, especially when combined with low CSF Aβ42, and high CSF heart fatty acid-binding protein23.