APOE and mucopolysaccharidosis type 2: The receptor‐binding portion of ApoE used here is able to form a high‐affinity binding complex with an octasaccharide HS fragment composed of four repeats of UA(2S)‐GlcNS(6S) (Libeu et al, 2001), which are abundant on endothelial cell surfaces and even more abundant in MPS II.