C9− ALS vs. HCs → ↓ Left hippocampus volume.C9+ ALS vs. HCs → ↓ Bilateral hippocampal volumes.Vertex‐wise shape analyses → Changes in the lateral and inferior part of the left hippocampus.↑ AD, MD, and RD in the hippocampus of C9+ ALS vs C9− ALS. The gene discussed is C9; the disease is Alzheimer disease.