Enzyme-replacement therapy in a 5-month-old boy with attenuated presymptomatic MPS I: 5-year follow-up.

Mucopolysaccharidoses type I (MPS I) is a progressive and multisystemic disease, even in its attenuated Hurler-Scheie forms. Clinical trials of enzyme-replacement therapy in MPS I have shown clinical benefit in patients with considerable preexisting disease, but no data exist on the effect of beginning enzyme replacement before the onset of significant clinical signs of disease. Here we present the 5-year follow-up of a boy with atteniated MPS I who had laronidase therapy initiated at the age of 5 months and compare his clinical course to that of his older sister, who began treatment at 5 years of age after she had developed typical signs of MPS I. After 5 years of treatment, the younger sibling has not developed any clinical manifestation of MPS I except for mild corneal clouding. In contrast, althought many of the other sibling's clinical features have improved after 5 years of treatment, her dysostosis multiplex, cardiac valve involvement, and corneal cluoding, althought stabilized, have persisted. We suggest that early treatment of attenuated MPS I may significantly delay or prevent the onset of the major clinical signs, substantially modifying the natural history of the disease.