Recently, pabinafusp alfa, a BBB-penetrating fusion protein consisting of an anti-human transferrin receptor (TfR) antibody and IDS, was approved in Japan for the treatment of patients with all, including neuronopathic, forms of MPS II [105,106,107,108,109,110,111,112,113,114]. The gene discussed is TFRC; the disease is mucopolysaccharidosis type 2.