18-year follow-up of enzyme-replacement therapy in two siblings with attenuated mucopolysaccharidosis I

Mucopolysaccharidosis type I (MPS I) is an autosomal recessive disorder caused by the deficiency of alpha-L-iduronidase and characterized by a progressive course with multisystem involvement. Clinically, MPS I is divided into two forms: (1) severe (Hurler syndrome), which presents in infancy and is characterized by rapid progressive neurological involvement; (2) attenuated (Hurler/Scheie and Scheie syndromes), which displays a slower progression and absent to mild nervous system involvement. The specific treatment for attenuated MPS I consists of enzyme-replacement therapy with laronidase (human recombinant alpha-L-iduronidase, Aldurazyme). We present updated data after 18 years of laronidase treatment in two siblings affected by the attenuated form of MPS I who started therapy at 5 months and 5 years of age, respectively. Clinical and laboratory data of the siblings show that long-term enzyme replacement therapy may improve/stabilize many symptoms already present at the time of the diagnosis and reduce the disease progression. This study confirms that early diagnosis and early initiation of enzyme-replacement therapy are essential to modify positively the natural history of the attenuated form of MPS I.