To address the critical role of disrupted mitochondrial fusion in neurodegeneration and other AD-related disorders, Jiang and colleagues knocked out Mfn2 in the hippocampus and cortex of mice and found that this ablation caused neuronal degeneration in vivo in a temporal order, and the pathological changes that they have highlighted are also seen during AD progression. This evidence concerns the gene MFN2 and Alzheimer disease.