In MS, the sNfL level increases at disease onset,13 is associated with MRI changes of disease activity and neurodegeneration14 and is sensitive to treatment effects.15,16 Serum NfL is becoming increasingly available and accessible in clinical practice.17,18 Yet, because serum-based biomarkers alone still face variability, low sensitivity to disease activity and imperfect assay standardization, incorporating complementary data (such as MRI metrics) can strengthen their clinical utility.19-21. This evidence concerns the gene NEFL and myeloid sarcoma.