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 This evidence concerns the gene NEFL and autoimmune polyendocrinopathy.