NEFL and motor neuron disorder: In the same vein, in the ongoing ATLAS trial, unaffected carriers of highly penetrant SOD1 variants associated with rapidly progressive motor neuron disease and whose blood neurofilament light chain (NfL) level rises above a pre-defined threshold, are randomized to receive tofersen (a SOD1 ASO) or placebo.19 Such use of NfL as a criterion for randomization depends on its established utility as a susceptibility/risk biomarker20—namely, that it predicts the likely timing of phenoconversion at an individual level.21