Overall, supplementation with DHA compared with placebo did not slow the rate of cognitive and functional decline in patients with mild to moderate Alzheimer disease, but while there was no DHA treatment effect on any outcome measure in the APOE4-positive group, those receiving DHA in the APOE4-negative group had a significantly lower decline in mean change in Alzheimer's Disease Assessment Scale-Cognitive Subscale score over 18 months vs. placebo group. Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.