Neurological MPS are characterized by the accumulation of heparan sulphate (HS) caused by a deficiency of α-l-iduronidase (MPS I), iduronate-2-sulfatase (MPS II), iduronate-2-sulfatase (MPS II), N-sulfoglucosamine sulfohydrolase (MPS IIIA), N-acetyl-α-d-glucosaminidase (MPS IIIB), acetyl-CoA:α-glucosaminide N-acetyltransferase (HGSNAT) (MPS IIIC), N-acetylglucosamine-6-sulfate sulfatase (MPS IIID), or β-glucuronidase (MPS VII) (2). Here, IDS is linked to mucopolysaccharidosis type 3D.