APOE and Alzheimer disease: 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.