Nonsense suppression therapy is a therapeutic approach aimed at treating genetic diseases caused by in-frame premature termination codons (PTCs; also commonly known as nonsense mutations). This approach utilizes compounds that suppress translation termination at PTCs, which allows translation to continue and partial levels of deficient protein function to be restored. We hypothesize that suppression therapy can attenuate the lysosomal storage disease mucopolysaccharidosis type I-Hurler (MPS I-H), the severe form of α-l-iduronidase deficiency. α-l-iduronidase participates in glycosaminoglycan (GAG) catabolism and its insufficiency causes progressive GAG accumulation and onset of the MPS I-H phenotype, which consists of multiple somatic and neurological defects. 60-80% of MPS I-H patients carry a nonsense mutation in the IDUA gene. We previously showed that 2-week treatment with the designer aminoglycoside NB84 restored enough α-l-iduronidase function via PTC suppression to reduce tissue GAG accumulation in the Iduatm1Kmke MPS I-H mouse model, which carries a PTC homologous to the human IDUA-W402X nonsense mutation. Here we report that long-term NB84 administration maintains α-l-iduronidase activity and GAG reduction in Iduatm1Kmke mice throughout a 28-week treatment period. An examination of more complex MPS I-H phenotypes in Iduatm1Kmke mice following 28-week NB84 treatment revealed significant moderation of the disease in multiple tissues, including the brain, heart and bone, that are resistant to current MPS I-H therapies. This study represents the first demonstration that long-term nonsense suppression therapy can moderate progression of a genetic disease. © 2013.