Mucopolysaccharidosis type IIIB (MPS IIIB) is an inherited metabolic disease caused by the deficiency of the enzyme α-N-Acetylglucosaminidase (NAGLU, EC: 3.2.1.50) required for the degradation of the glycosaminoglycan (GAG) heparan sulfate (HS) [1,2]. The gene discussed is NAGLU; the disease is metabolic disease.