More than 25 risk genes have been identified for Alzheimer’s disease, with APOE4 contributing the highest risk.8 Besides examining the association of genetic variants with risk for Alzheimer’s disease,9 several post-mortem studies of human brain report differential expression of implicated candidate genes in Alzheimer’s disease, including APOE and CD33.10,11 Many studies have explored brain imaging findings, including brain metabolism, in cognitively unimpaired individuals with various genotypes related to risk for Alzheimer’s disease, particularly of APOE. The gene discussed is CD33; the disease is early-onset autosomal dominant Alzheimer disease.