THE ULTRASTRUCTURE OF SKIN FROM A PATIENT WITH MUCOPOLYSACCHARIDOSIS IIID

Mucopolysaccharidosis IIID (MPS-IIID) is the rarest of the MPS-III syn dromes, It is caused by deficient activity of lysosomal N-acetylglucos amine-6-sulfatase (G6S). To date, the clinical and biochemical feature s of seven patients with MPS-IIID have been reported, but no biopsy or autopsy findings have been described. The purpose of this report is t o define the ultrastructure of affected cells seen in a skin biopsy fr om a 14-year-old boy. The child presented with progressive mental dete rioration, hyperactivity and mild to moderate dysmorphism. The diagnos is of a mucopolysaccharidosis was suggested, but the initial urine ana lyses were negative for elevated mucopolysaccharides, and only the thi rd analysis showed abnormal excretion of heparan sulfate, Because of t he diagnostic difficulties posed by this case, a skin biopsy was perfo rmed for morphological and biochemical studies. Numerous vacuoles were noted in Schwann cells, fibroblasts, smooth muscle cells? eccrine gla nd and ductal epithelium in resin-embedded sections stained with tolui dine blue. Ultrastructurally, many lysosomes were distended with abund ant, fibrillar material. Occasionally, lamellated membranous structure s were present within the same lysosomes, These findings are consisten t with those seen in other forms of MPS, in which the lysosomal storag e occurs predominantly, but not exclusively, in mesenchymal cells. Fur thermore, deficient activity of G6S was confirmed in cultured skin fib roblasts, This study demonstrates that electron microscopy of skin bio psies is a useful method for identification of patients with clinical features of MPS-IIID whether or not heparan sulfaturia is present.