In MPS IIIA (OMIM #252900) homozygosity for the missense mutations c.897C > T, p.(Ser298Pro) and c.617G > C, p.(Arg206Pro) in the sulfamidase (SGSH) gene resulted in an attenuated phenotype with a later onset of regression, a slower progression of neurocognitive decline, and a longer survival [12–14]. The gene discussed is SGSH; the disease is mucopolysaccharidosis type 3A.