ARSG and mucopolysaccharidosis: Nevertheless, since both GAG storage and deficiency in activity of an enzyme involved in GAG degradation are required to make an MPS diagnosis, in our opinion, despite mice with Arsg dysfunction resembling those used as models in other subtypes of MPS III, classification of the corresponding disease in humans as MPS IIIE should be considered only if patients are described with ARSG variants as the only genetic defect, while developing biochemical features and symptoms characteristic of MPS.