[Mucolipidosis type III (case report)]

A six-year-old boy with mucolipidosis type III or pseudo Hurler polydystrophy is described. The disease is manifested by multiple progressive joint contractures, especially of fingers, presenting as claw hands. The diagnosis of mucolipidosis was established after exclusion of rheumatoid arthritis and mucopolysaccharidosis. In serum and medium of cultured skin fibroblasts, high catalytic activities of several lysosomal enzymes with strikingly decreased values in fibroblast homogenate were found. In most lysosomal diseases gene mutations cause reduced or absent activity of a specific enzyme. In mucolipidosis type III, a basic biochemical disorder is the absence of mannose-6-phosphate, a marker that enables lysosomal membrane receptors to recognize lysosomal enzymes. The transport of lysosomal enzymes across the lysosomal membrane is therefore defective. These and several other metabolic diseases are thus categorized as the disorders of the lysosomal enzyme transport. A genetic and biochemical heterogeneity, as well as clinical manifestations, are described in more detail.