Neurofilament light chain (NfL) has gathered increasing interest in A-T and other neurodegenerative diseases such as Hereditary Motor and Sensory Neuropathy (Charcot-Marie-Tooth disease), multiple sclerosis and Parkinson’s disease, suggesting that elevated levels in the blood and cerebrospinal fluid (CSF) are associated with axonal damage [22–24]. This evidence concerns the gene NEFL and neuropathy, hereditary motor and sensory, type 6A.