GALNS and mucopolysaccharidosis type 4A: Due to allelic heterogeneities in the GALNS gene, MPS IVA manifests across a broad spectrum of phenotypes, ranging from severe or ‘classical’ forms, characterized by early clinical manifestations (before 1 year of age) and rapid progression of musculoskeletal symptoms, to a later onset and slowly progressing ‘mild’ disease, characterized by less significant bone involvement (‘non-classic’ disease) [4].