HS3ST4 and Alzheimer disease: Three isoforms of the heparan sulfate 3-O sulfotransferases (HS3ST2, HS3ST4 and HS3ST5) are predominately expressed in AD-relevant brain regions [27–29], with HS3ST2 and HS3ST4 mRNA levels being reported to be significantly increased in the AD hippocampus [21].