All types of Sanfilippo disease (MPS III) are due to different defects in the degradation of heparan sulphate. Clinically the four subtypes (A, B, C and D) are indistinguishable from each other. As in other MPS there is a gradation of severity from mild to severe for all four types. Patients have progressive mental handicap but usually only mild somatic and skeletal involvement. Presentation is usually between 2 and 6 years of age with hyperactivity, aggressive behaviour or developmental delay. The facies may be somewhat coarse but there is usually no lumbar gibbus or corneal clouding. Hepatomegaly is occasionally present but is mild. Height is usually normal. Radiologically there is mild generalised dysostosis.
Heparan sulphamidase is the primary deficiency in Sanfilippo disease type A. Deficiency of lysosomal a-N-acetylglucosaminidase is the primary defect in Sanfilippo disease type B. Deficiency of glucosamine N-acetyltransferase is the primary defect in Sanfilippo disease type C (MPS IIIC). Deficiency of N-acetylglucosamine 6-sulphatase is the primary test in Sanfilippo disease type D (MPS IIID) but this assay is not available in the SAS laboratory.