TFRC and mucopolysaccharidosis type 2: In another instance, iduronate 2-sulfatase, a lysosomal enzyme deficient in mucopolysaccharidosis type II (MPS II), fused to a moderate-affinity, monovalent TfR-binding enzyme showed enhanced brain exposure from internalization by parenchymal cells and significant substrate reduction in the CNS of an MPS II [180].