Contributor: Gordon K. Klintworth
Mucopolysaccharidosis type I  includes three allelic clinically different phenotypes (mucopolysaccharidosis type I-H, mucopolysaccharidosis type I-S, and mucopolysaccharidosis type I-H/S) that resemble each other biochemically. These mucopolysaccharidoses are caused by different mutations in the IDUA gene that encodes for alpha-L-iduronidase. These lysosomal storage diseases vary in severity with mucopolysaccharidosis type I-H being the most serious, and mucopolysaccharidosis type I-S the least severe. A separate genetic mutation seems to be responsible for the different disorders and only one clinical phenotype develops in affected families. The ocular manifestations include corneal clouding, a pigmentary retinopathy, bilateral narrow or closed angle glaucoma [glaucoma - narrow angle, glaucoma - closed angle], and chronic papilledema with optic atrophy. Histologically, the lesions in the different variants of mucopolysacharidosis type I are indistinguishable from each other. By light microscopy the keratocytes and basal cells of the corneal epithelium are vacuolated and stain with reagents that demonstrate glycosaminoglycans. Bowman layer has sometimes been attenuated. Multiple single membrane-delimited vacuoles containing fibrillogranular material appear in fibroblasts and the epithelium of the conjunctiva. In mucopolysaccharidosis type I the tears can be used to evaluate the efficiency of bone marrow transplantation.