Promising efficacy and safety results were recently observed in Phase 2/3 clinical trial of JCR Pharmaceuticals’ anti-TfR-coupled IDS protein, which was recently conducted in 28 Japanese patients with Hunter syndrome (Okuyama et al., 2021), and has recently resulted in the first approval of TfR antibody—enzyme fusion protein for facilitated brain delivery. This evidence concerns the gene TFRC and mucopolysaccharidosis type 2.