It is known that in PD α-synuclein aggregation occurs mainly in neurons with high energy turnover in less myelinated axons,23 whereas NfL is mainly expressed in larger myelinated axons.24 Thus, our data are consistent with the concept that increases in NfL are not disease specific, but reflect the magnitude and perhaps the tempo of neuronal damage of larger myelinated axons in any disease entity. The gene discussed is SNCA; the disease is Parkinson disease.