The focal lesions of the skin and mucosae of this rare disease, that has been described as juvenile hyalin fibromatosis, are initially in moderately elevated plaques, that evolve to form nodules in the dermis. The fundamental defect, possibly of autosomal recessive inheritance, is a disturbance in the metabolism of the mucosaccharides. There is an accumulation, both intracellularly, in membrane-limited vacuoles, and extra-cellulary, of fibrilar glycoprotein complexes, the saccharides of which are both neutral and acidic, non-sulfated and sulfated. The material accumulated in the interstitium has hyalin aspect and is poorer in sulfated mucosaccharides than the intracellular vacuoles. The defect manifests itself primarily in the mesenchymal perviascular cells, leading to their proliferation.