Sanfilippo B syndrome (MPS III B): mild and severe forms within the same sibship

Abstract
Clinical heterogeneity for Sanfilippo B syndrome (mucopolysaccharidosis type III B; MPS III B) in the same family was not previously reported. Two clinically severe cases and 1 clinically mild case of MPS III B are described in an Italian sibship. N-acetyl-.alpha.-D-glucosaminidase activity was not detected in the sera of either the severe or mild cases. Mucopolysacchariduria mainly due to heparan sulfate excretion was consistently high in the severely affected patients and extremely variable in the mildly affected one.