APOE and early-onset autosomal dominant Alzheimer disease: However, the diagnostic evaluation makes this possibility extremely unlikely: given the strong family history of dementia, the ApoE4 heterozygosity, markedly positive amyloid PET scan, the FDG-PET scan characteristic of Alzheimer's disease with reduced glucose utilization in a temporoparietal distribution, the abnormal neuropsychological testing, and the MRI showing hippocampal volume at 17th percentile for age, the possibility that the underlying pathological process was something other than Alzheimer's disease is remote.