Mucopolysaccharidosis I: Characterized by a wide range of phenotypic involvement with three major recognized clinical entities: Hurler (MPS IH), Scheie (MPS IS), and Hurler-Scheie (MPS IH/S) Syndromes. All three variants are caused by a deficiency of α-L-iduronidase. Hurler and Scheie Syndromes represent phenotypes at the severe and mild ends of the MPSI clinical spectrum, respectively, and Hurler-Scheie Syndrome is intermediate in phenotypic expression. MPS I is more frequent than MPS II (Hunter Syndrome), which has no corneal clouding and pursues a slower course. The clinical characteristics are discussed under Mucopolysaccharidoses.
MPS II (Hunter Syndrome): Caused by a deficiency of iduronate sulfatase with storage of dermatan sulfate and heparan sulfate in many tissues. It is similar to MPS I, except for the absence of corneal clouding and slower progression of the course of the disease and central nervous system deterioration. Two types are recognized, both of which are normal at birth: severe (MPS IIA), which is characterized mainly by mental retardation and progressive physical deterioration and early death, and a mild form (MPS IIB), in which patients may survive into adulthood. Onset of MPS IIA occurs between 2 and 4 years of age; deterioration, chronic diarrhea, recurrent ear infections, hearing impairment, and communicating hydrocephalus with increased intracranial pressure are progressive features, with death occurring between the ages of 10 and 15 years. Obstructive airway disease caused by hypertrophied adenoids and tonsils. Cardiac valvular dysfunction, myocardial thickening, pulmonary hypertension, coronary disease, and myocardial dysfunction may complicate the illness. MPS IIB is milder without mental retardation. Symptoms include hearing impairment, carpal tunnel syndrome, joint stiffness, discrete corneal opacities, and papilledema. Death may occur in young adulthood and can be caused by airway obstruction or cardiac failure. Laryngoscopy and tracheal intubation are usually very difficult.
MPS III (Sanfilippo Syndrome): Autosomal recessive inheritance inborn error of metabolism with a deficiency of the intralysosomal enzymes involved in heparan sulfate (HS) degradation. Affected infants appear normal at birth, with slowing of development taking place at about 1 to 2 years of age, occasionally not becoming apparent until early school age. Behavioral disorders, mental deterioration, and loss of motor skills are the principal features, with hirsutism, macrocephaly, and limited joint movements. Four biochemically distinct types, each with a different enzyme deficiency, are recognized: A, B, C, and D. The phenotype is similar in all four types and consists mainly of some facial coarsening with dull appearance, slightly sunken nasal bridge, and abundant scalp hair. Early development is usually normal, followed between the ages of 2 and 6 years by mainly behavioral disorders with progressive loss of mental and motor skills with spastic diplegia. The patient eventually becomes bedridden. Death usually occurs between 10 and 20 years of age. Type A has the most severe course with the earliest onset and mortality. Type A is caused by heparan sulfatase (EC 188.8.131.52) deficiency. Type B is caused by N-acetyl-alpha-D-glucosaminidase (EC 184.108.40.206) deficiency. Type C is caused by ...