Genome-wide association studies with pairwise associations between phenotypes and genetic variants provide a framework for brain imaging genetics. When a genetic variant correlates with both a disease and with an image-derived phenotype, the disease effect may be modulated by the image-derived phenotype. The LIFO (last in, first out) network is a brain network that can degenerate early and can be operationalized as an image-derived phenotype. LIFO is associated with Alzheimer's disease, and Alzheimer's disease is also associated with the MAPT genetic cluster. In collaboration with Oxford's Wellcome Centre for Integrative Neuroimaging (WIN), we analyze the LIFO-MAPT-Alzheimer's disease triangle and find an effect using VanderWeele mediation. The analysis is complicated by the non-binary nature of the genotype, and also by chromosome 17 inversion.