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University of Minnesota Hospital/Fairview, Minneapolis, MN, USA.
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Editor’s note: Dysfunction of cardiac valves (stenosis and regurgitation; mainly of left-sided atrioventricular and semilunar valves) is common in patients with severe mucopolysaccharidosis type I (MPS IH; Hurler syndrome), and is not improved by hematopoietic stem cell transplantation or enzyme replacement therapy. Valve thickening in MPS IH patients is partly due to the presence of glycosaminoglycan (GAG)-laden cells (“clear” or “Hurler” cells) deep within the valve. The identity, origin, and function of these cells, initially considered to be either histiocytes or fibroblasts, remain largely unstudied. Semilunar valves from normal children (which contain no GAG-laden cells) contain small spindle-shaped cells, termed valvular interstitial cells (VICs), that are thought to be responsible for the growth and repair of the valves.