AD: Alzheimer’s disease; MCI: moderate cognitive impaired; CU: cognitively unimpaired; CN: cognitively normal; SUVR: standardized uptake value ratios; PCC: posterior cerebral cortex; PET: positron emission tomography; MMSE: Mini-Mental-State Examination; CDR-SOB: The clinical dementia rating-sum of boxes; PC: principal component; SV2A: synaptic vesicle glycoprotein 2A; FTLD: frontotemporal lobar degeneration; ROI: region of interest; FDG: fluorodeoxyglucose; FBB: florbetaben; aMCI: amnestic mild cognitive impairment. The gene discussed is SV2A; the disease is Alzheimer disease.