Relative to controls, greater Alzheimer’s disease pathology (lower amyloid-β42/amyloid-β40, higher phosphorylated-tau-181) and synaptic degeneration (neurogranin) biomarker concentrations were associated with more adverse white matter metrics (e.g. lower neurite density, higher mean diffusivity) in patients with asthma. Here, NRGN is linked to early-onset autosomal dominant Alzheimer disease.