Our group and others have previously shown that the CSF concentration of NfL is increased in APD but not in PD3,4 and that NfL in CSF can discriminate between PD and APD with a high degree of diagnostic accuracy.5, –, 7 However, lumbar puncture is not easily implemented in the primary care setting and many patients feel apprehensive about lumbar puncture, reducing the clinical usefulness of these findings. The gene discussed is NEFL; the disease is Parkinson disease.