Although in vitro assessment showed successful HR of the GALNS cDNA expression cassette, leading to the long-term biochemical recovery of the MPS IVA fibroblast phenotype [37], in vivo assessment, using the ROSA26 locus as a safe harbor, only partially rescued bone lesions in MPS IVA mice [36], highlighting the need for a novel strategy. The gene discussed is GALNS; the disease is mucopolysaccharidosis type 4A.