Table 1.

Classification of Mucopolysaccharidosis (MPS)

Type of MPS	Deficient Enzyme	Accumulated GAG	Age of onset of systemic features	Progression	Prognosis
IH - Hurler IHS - Hurler-Scheie IS - Scheie	α-l-iduronidase	HS, DS	IH: 1-2 years IHS: 3-7 years IS: 5-13 years	IH dies in 1st decade without treatment; HIS & IS have a longer lifespan	Mortality depends on the age of onset of symptoms and progression. Ocular symptoms are seen in all 3 phenotypes.
II - Hunter	Iduronate-2-sulfatase	HS, DS	Onset at birth but presents at 2-4 years	Progresses through the 1st decade	Mortality by 2nd decade except for mild cases which survive up to 6th-7th decade. Posterior segment ocular manifestations more prominent.
IIIA - Sanfilippo A IIIB - Sanfilippo B IIIC -Sanfilippo C IIID - Sanfilippo D	Heparan-N-sulfatase α-N-Acetylglucosaminidase α-glucosaminide acetyltransferase N-acetylglucosamine-6-sulfatase	HS HS HS HS	2-6 years	Initially presents with neurocognitive symptoms such as language delay, behavioral issues, and hyperactivity with progressive gait disorders and pyramidal signs.	Vegetative state and death by early 30s
IVA - Morquio A IVB - Morquio B	N-acetylgalactosamine-6-sulfatase β-galactosidase	KS, C6S KS	After 1st year of life	Progressive skeletal abnormalities; wheelchair-bound by teenage years	Mortality occurs due to respiratory obstruction and cervical spinal anomalies by 3rd decade of life.
VI - Maroteaux Lamy	N-acetylgalactosamine-4-sulfatase	DS, C4S	2 years	Progressive growth retardation	Mortality in late teens up to 5th decade due to cardiopulmonary complications
VII - Sly	β-glucuronidase	DS, C6S, C4S, KS	Variable	Not well understood due to rarity of disease	Can vary from prenatal death to survival up to 5th decade
IX - Natowicz	Hyaluronidase	Hyaluronan	Rare reports; earliest at 14 years old	Progressive craniofacial and skeletal abnormalities	Not well understood

HS, Heparan sulfate; DS, Dermatan sulfate; KS, Keratan sulphate; C6S, Chondroitin-6-sulfate; C4S, Chondroitin-4-sulfate