Examples are alpha-L-iduronidase deficiency causing mucopolysaccharidosis type I, an inherited lysosomal disease45, and mutant β-galactosidase44,46 triggering GM1 gangliosidosis and mucopolysaccharidosis type IVB, also known as Morquio B disease44,46. The gene discussed is IDUA; the disease is mucopolysaccharidosis type 4B.