Free sialic acid storage disease. A new Italian case.

Increased amounts of free sialic acid were found in cultured fibroblasts and urine of a 4-year-7-month-old Italian boy with mental retardation, hypotonia, failure to thrive, coarse facial features, convergent strabismus, pale skin and fair hair. Ultramicroscopic examination of conjunctival and skin tissues showed a number of membrane-bound vacuoles containing low-density granular material in the cytoplasm of the fibroblasts. The clinical, biochemical and ultrastructural findings are similar to those described in Salla disease. Neuraminidase activity is normal. The molecular basis of the sialic acid storage disease is not known. Evidence for defective transport of sialic acid across the lysosomal membrane has been demonstrated in the patient's fibroblasts. It is possible that this might represent the metabolic abnormality.