Early disease course is unaltered in mucopolysaccharidosis type IIIA (MPS IIIA) mice lacking α-synuclein

Sanfilippo syndrome (mucopolysaccharidosis type IIIA; MPS IIIA) is an inherited paediatric-onset neurodegenerative disorder caused by the lysosomal deficiency of sulphamidase with subsequent accumulation of heparan sulphate. The pathological mechanisms responsible for clinical disease are unknown; however, intraneuronal accumulation of aggregation-prone proteins such as α-synuclein, phosphorylated tau and amyloid precursor protein suggests inefficient intracellular trafficking and lysosomal degradation.

To investigate the contribution the accumulating α-synuclein plays in early symptom emergence that is, impaired cognition, reduced anxiety and motor deficits, first detectable between 3-5 months of age.

We have crossed congenic MPS IIIA mice with α-synuclein-deficient (Snca^tm1Rosl /J) mice and evaluated phenotype and brain disease lesions.

In a battery of behavioural tests performed on mice aged 12-22 weeks, we were unable to differentiate α-synuclein-deficient MPS IIIA mice from those with one or both copies of the α-synuclein gene; all three affected genotypes were significantly impaired in test performance when compared to wild-type littermates. Histological studies revealed that the rate, location and nature of deposition of other proteinaceous lesions, the disruption to endolysosomal protein expression and the inflammatory response seen in the brain of α-synuclein-deficient MPS IIIA mice reflected that seen in MPS IIIA mice homo- or heterozygous for α-synuclein.

Deletion and/or deficiency of α-synuclein does not influence clinical and neuropathological disease progression in murine MPS IIIA, demonstrating that in and of itself, this protein does not initiate the cognitive and motor symptoms that occur in the first 5 months of life in MPS IIIA mice.