Cognitive development in patients with Mucopolysaccharidosis type III (Sanfilippo syndrome)

Background: Mucopolysaccharidosis type III (MPS III, Sanfilippo syndrome) is a lysosomal storage disorder caused by a deficiency of one of the enzymes involved in the degradation of heparan sulfate. MPS III is characterized by progressive mental deterioration resulting in severe dementia. A number of potentially disease-modifying therapies are studied. As preservation of cognitive function is the ultimate goal of treatment, assessment of cognitive development will be essential in order to evaluate treatment efficacy. However, no large scale studies on cognitive levels in MPS III patients, using formal psychometric tests, have been reported. Methods: We aimed to assess cognitive development in all 73 living patients with MPS III in the Netherlands. Results: Cognitive development could be assessed in 69 patients. In 39 of them developmental level was estimated >3 months and formal psychometric testing was attempted. A remarkable variation in the intellectual disability was detected. Conclusions: Despite special challenges encountered, testing failed in only three patients. The observed broad variation in intellectual disability, should be taken into account when designing therapeutic trials.