Neurofilament light chain (NF-L), a marker of axonal degeneration of large-calibre myelinated axons, is a reliable differentiator of APS, PD and controls in cerebrospinal fluid (CSF)3 4 and plasma.5 However, the level of NF-L does not differentiate between PSP, CBS and MSA,3 and it is also raised in other neurodegenerative disorders such as frontotemporal dementia (FTD).6 The gene discussed is NEFL; the disease is supranuclear palsy, progressive, 1.