Contributor: Gordon K Klintworth
Mucopolysaccharidosis type III (Sanfilippo syndrome) is a mucopolysaccharidosis characterized by the excretion in the urine of heparan sulfate. Four phenotypically indistinguishable non-allelic forms involving different enzymes are recognized: mucopolysaccharidosis type IIIA, mucopolysaccharidosis type IIIB, mucopolysaccharidosis type IIIC, and mucopolysaccharidosis type IIID.  A deficiency of a particular enzyme leads to an accumulation of partially degraded fragments of heparan sulfate in the tissues, the abnormal appearance of heparan sulfate in the urine and a slowly progressive cerebral atrophy. Increased levels of gangliosides accumulate in the brain. The disease is usually diagnosed at 2-6 years of age and is ultimately fatal. The clinical manifestations include hyperactivity, attention deficit disorder, developmental delay, hirsutism, coarse facial features and hepatosplenomegaly. A progressive neurological deterioration with severe mental retardation begins in childhood and includes aphasia, vasomotor instability, epilepsy and dementia. Some attributes of the syndrome resemble those of  mucopolysaccharidosis type I-H and mucopolysaccharidosis type II (except with less dwarfism).