Objective: Mucopolysaccharidosis types IIIA through IIID (Sanfilippo syndrome) are caused by deficiencies of enzymes involved in the degradation of heparan sulfate. The onset and severity of the disease are highly variable. The purpose of this study was to describe the natural course of mucopolysaccharidosis type IIIA in a large cohort of patients.
Patients and methods: The natural course of mucopolysaccharidosis type IIIA was assessed in 71 patients by using a detailed questionnaire and a 4-point scoring system and compared with the course of the disease in 14 patients with mucopolysaccharidosis type IIIB and 4 patients with mucopolysaccharidosis type IIIC.
Results: In the cohort of patients with mucopolysaccharidosis type IIIA, first symptoms of disease were observed, on average, at 7 months of age. Speech and motor development were delayed in 66.2% and 33.9% of patients, respectively. The median age at diagnosis was 4.5 years. The onset of regression in speech, motor, and cognitive function was observed at an average age of 3.3 years. The loss of all 3 of the assessed abilities was observed at an average age of 12.5 years. Speech was lost before motor and cognitive functions. In a small group of patients who were >12.5 years of age (9.9%), speech, motor, and cognitive skills were partially preserved up to a maximum age of 23.8 years.
Conclusions: To our knowledge, this is the first systematic and comprehensive study on the natural course of mucopolysaccharidosis type IIIA. The 4-point scoring system may be used to classify patients into groups with a rapid or slower course of the disease. This may have an important impact on parental counseling as well as therapeutic interventions.