The invention is based at least in part on the finding that a dimeric version of a BBB transmigrating antibody (e.g. theTMEM30A (CDC 50A) binding antibody FC5) was found to greatly enhance transport across the BBB as compared to monovalent FC5 V The invention provides inter alia molecules that increase transport of pharmacologically active agents across the blood brain barrier methods for increasing transport across the blood brain barrier and methods of treatment of disorders or diseases having a neurological component.