APOE is involved in both the clearance of Aβ95,96 and the transport of phosphatidylcholine,97 and carrying the ε4 allele of the APOEgene is the largest genetic risk factor for late-onset Alzheimer’s disease.98,99 Studies have also reported increased degeneration of the basalforebrain cholinergic system in APOE4 carriers compared withnon-carriers.59,100 Unsurprisingly, the abnormal CSFgroup contained the majority of the APOE4 carriers in our sample, with onlyeight normal CSF individuals having one or more ε4 alleles. Here, APOE is linked to early-onset autosomal dominant Alzheimer disease.