Neurofilament light chain (NfL), an axonal structural protein, is an established biomarker for axonal damage and was shown to be a response biomarker in hereditary transthyretin-mediated (hATTR) polyneuropathy and vasculitis neuropathy, and in selected cases, for chronic inflammatory demyelinating polyneuropathy (CIDP) [12–15]. The gene discussed is NEFL; the disease is chronic inflammatory demyelinating polyradiculoneuropathy.