A small study involving 52 people aged 32-72 has found that those whose parents both had Alzheimer's disease showed more severe abnormalities in brain volume and metabolism and 5-10% more amyloid plaques in certain brain regions, compared to those with either a father or mother, or neither parent, with the disease. There were 13 in each group.
Consistent with previous research, those whose mother had Alzheimer's disease showed a greater level of the Alzheimer's disease biomarkers than those whose father had the disease.
(2014). Brain imaging of cognitively normal individuals with 2 parents affected by late-onset AD.
Neurology. 82(9), 752 - 760.