IDUA and mucopolysaccharidosis type 1: The first BBB Trojan horse fusion protein tested in human clinical trials was a fusion protein of iduronidase (IDUA), the lysosomal enzyme mutated in Mucopolysaccharidosis Type I (MPSI), and a HIRMAb, and this fusion protein is alternatively designated as the HIRMAb-IDUA fusion protein or valanafusp alpha [141].