NEFL and Charcot-Marie-Tooth disease type 1A: NfL is indicated to be a good biomarker of axonal degeneration in CMT1A and other CMT subtypes, as well as a range of neurological diseases including ALS,41 frontal temporal dementia,42 and MS.43 NfL may prove a good efficacy biomarker in CMT; interestingly, NfL plasma levels were elevated in a mouse model of CMT4C and were returned to normal with successful gene therapy treatment.44 Further studies are required to determine its stability in CMT1A longitudinal samples.