ABCD4 and Alzheimer disease: Estimates of IBD sharing for the 10 participants with the ABCD4 variants were only slightly higher (mean [SD] π̂ = 0.015 [0.028]) and for the 8 participants with AD and the CELSR1 and GTSE1 variants (mean [SD] π̂ = 0.008 [0.015]) were lower than genome-wide IBD sharing, suggesting that they are not more closely related to each other than to all participants.