We saw a negative relationship between FA and NfL (CSF) levels in the corpus callosum at a significance level of P = 0.06, FWE corrected—interesting given the evidence of early callosal degeneration in HD.40, 41 This was coupled with a pattern of higher NfL levels and both higher diffusvity, that is, MD, AD, and RD and increased axonal dispersion in the external capsules surrounding the striatum. This evidence concerns the gene NEFL and Huntington disease.