A recent study found that young adults with the gene mutation that causes Huntington’s disease who were ∼25 years from their predicted motor onset had significantly elevated concentrations of plasma neurofilament light chain protein compared with controls.18 Those results may indicate that the neurodegenerative changes observed in Huntington’s disease can be measured more than two decades before the onset of motor symptoms of Huntington’s disease. This evidence concerns the gene NEFL and Huntington disease.