APOE and early-onset autosomal dominant Alzheimer disease: Being female and being scanned at an older age over the 2-year assessment period were independently associated with NAWM microstructural differences, but this was explained by differences in cerebral small vessel disease; no evidence emerged for associations between NAWM and childhood cognition, education and the biggest genetic risk factor for ‘sporadic’ Alzheimer’s disease (APOE-ɛ4).