ABSTRACT
Hunter [1], in 1917, described two brothers with what is now known as mucopolysaccharidosis type II. Patients with the Hunter disease have clinical features similar to those of Hurler disease, although usually they are less severely affected. Patients have been classified clinically into mild and severe forms, although the two cannot be distinguished on the basis of enzyme activity. The advent of molecular analysis and extensive heterogeneity may make this classification obsolete. Patients with this disease were found, by Dorfman and Matalon [2] and by Muir [3], to excrete dermatan sulfate and heparan sulfate just like those with Hurler disease. It was in studies of Hunter and Hurler cells that Fratantoni, Hall and Neufeld [4] first found the correction factors from each that corrected the defective excess accumulation of sulfate in the other; thus Hurler cells could correct Hunter cells and vice versa, and the Hunter corrective factor would correct Hurler and other MPS cells, but not Hunter cells [5]. The Hunter factor was identified as iduronate sulfatase [6] (Figure 79.1), the enzyme that catalyzes the release of sulfate from the iduronate sulfate moieties of dermatan and heparan sulfates. This is the site of the molecular defect in Hunter disease. Thus the defect in MPS II is
in the first step in the enzymatic breakdown of these mucopolysaccharides.
