GUSB and mucopolysaccharidosis type 7: Mucopolysaccharidosis VII (MPS VII), also known as Sly syndrome, is a heterogeneous, progressive, metabolic disorder caused by autosomal recessive inherited loss of function mutations at the GUSB gene (OMIM# 253220), leading to deficiency of the lysosomal enzyme β-glucuronidase (GUS: β-D-glucuronoside glucuronosohydrolase) [1–3] and consequent storage of glycosaminoglycans (GAGs).