NEFL and juvenile Huntington disease: At this stage, Huntington's disease pathology has already had a widespread effect on brain structure, with extensive evidence of striatal atrophy and white matter degeneration.4, 5 Elevations in plasma neurofilament light protein (NfL) a marker of axonal damage, were noted in the TRACK-HD cohort7 and such biofluid markers might be among the earliest detectable alterations in Huntington's disease.8