Neurofilament light chain reflects motor impairment in myotonic dystrophy type 1

Introduction Myotonic dystrophy type 1 (DM1) is a genetic disorder caused by CTG trinucleotide repeat expansion in the dystrophia myotonica-protein kinase (DMPK) gene and is characterized by progressive muscle weakness with multisystemic involvement, including the central nervous system (CNS). Neurofilament light chain (NfL) has emerged as a biomarker of neuroaxonal damage in various neurological conditions. This study aimed to evaluate plasma NfL as a biomarker of disease severity by examining its association with motor function in ambulatory patients with DM1. Methods Thirty-three DM1 patients and 31 controls were enrolled. Plasma NfL levels were measured, and clinical variables including age, sex, age at onset, and disease duration were collected. Motor function was assessed using the Muscular Impairment Rating Scale (MIRS) and the 6-min walk test (6MWT). Associations between NfL levels and clinical measures were analyzed using partial correlation based on Kendall's Tau with adjustment for age. Results Age-adjusted analyses demonstrated a significant positive correlation between NfL levels and MIRS scores (τ = 0.387, p = 0.002) and a significant negative correlation with 6MWT performance (τ = −0.344, p = 0.014). Disease duration was also positively associated with age-adjusted NfL levels (τ = 0.334, p = 0.007). Although NfL levels showed a negative correlation with peroneal CMAP amplitudes, this association was not significant after age adjustment. Conclusion Plasma NfL levels were associated with disease duration and motor function severity in DM1. These findings suggest that NfL may serve as a biomarker reflecting not only neuroaxonal damage but also motor impairment in DM1. Larger longitudinal studies are warranted to validate these findings.