After adjustment for age, serum NfL was on average 2.1 times higher (CI: 1.6;2.7, p-value: < 0.0001) in DM I, compared to levels in healthy controls, 1.4 times (CI: 1.2;1.7, p-value: < 0.0001) in DM 2/PROMM, 1.4 times (CI: 1.1;1.9, p-value: 0.0227) in FSHD and 3.2 times (CI: 2.7;3.8, p-value: < 0.0001) in the Mito-patient cohort. This evidence concerns the gene NEFL and facioscapulohumeral muscular dystrophy.