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. The gene discussed is NEFL; the disease is amyotrophic lateral sclerosis.