APOE and early-onset autosomal dominant Alzheimer disease: Transgenic mice with high levels of the apolipoprotein E gene APOE4 (a risk factor for Alzheimer's disease) and given a diet with low docosahexaenoic acid (an omega-3 fatty acid) had olfactory loss and memory loss along with an increase in IBA-1, an inflammatory factor, in the olfactory bulb.