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The Dwarf Pony

Mucopolysaccharidosis Type III

The subtypes of mucopolysaccharidosis III (MPS III) A,B,C and D are caused by lysosomal enzymes that are responsible for the degradation of heparan sulfate, an essential component of nerve cell membranes. This explains why in this mucopolysaccharidosis predominantly the central nervous system is affected and the patients have only slight dysmorphic features. First symptoms such as agitated behaviour and learning difficulties, mainly regarding speech development, appear at the age of 3-5 years. Later on epileptic seizures occur, at the end the patients get tetraspastic, most die at the age of around 20 years. The subtypes A.B,C and D do not show any difference in clinical phenotype.

Synonym: Sanfilippo syndrome

Etiology:
Disease
Mucopolysaccharidosis Type IIIA. Deficient enzyme: Heparan-sulfamidase
Mucopolysaccharidosis Type IIIB. Deficient enzyme: N-acetyl-alpha-glucosaminidase
Mucopolysaccharidosis Type IIIC. Deficient enzyme: N-acetyltransferase
Mucopolysaccharidosis Type IIID. Deficient enzyme: N-acetyl-glucosamin-6-sulfate-sulfatase

Gene:
Disease
Mucopolysaccharidosis Type IIIA. Gene: SGSH
Mucopolysaccharidosis Type IIIB. Gene: NAGLU
Mucopolysaccharidosis Type IIIC. Gene: HGSNAT
Mucopolysaccharidosis Type IIID. Gene: GNS

Mode of inheritance: Autosomal recessive

Phenotypes:

Severe form
Attenuated form

Leading symptoms:
Severe form
(Age of onset: )

Psychomotor development delay/ regression
Behavioral disorder
Hyperaktivity
Sleep disorder
Epilepsy
Joint contractures

Attenuated form
(Age of onset: childhood/ adolescence)

Loss of cognitive and motor skills
Psychiatric symptoms

Diagnostics:

Measurement of the activity of heparan-sulfamidase (Type IIIA), N-acetyl-alpha-glucosaminidase (Type IIIB), N-acetyltransferase (Type IIIC), N-acetyl-glucosamin-6-sulfat-sulfatase (Type IIID) in leukocytes or serum or plasma
Molecular genetic analysis of the appropriate gene: SGSH, NAGLU, HGSNAT, GNS

Therapy:
Only symptomatic