Infantile form of sialic acid storage disorder: clinical, ultrastructural, and biochemical studies in two siblings.

We describe two sibs with coarse facies, hepatosplenomegaly, prominent psychomotor retardation and unexpectedly fair complexion. Ultrastructural studies of conjunctival, skin, bone marrow and liver biopsies from these individuals showed generalized lysosomal storage of polysaccharide-like material, i.e., membrane bound inclusions containing sparse, fibrillo-granular material. Biochemical analyses of urine and cultured fibroblasts from these patients revealed increased levels of free (unbound) sialic acid. The ultrastructural and biochemical findings in these sibs are similar to those previously found in Salla disease, however, the clinical course is much more severe. It is concluded that these children represent a new pathogenetic entity whose basic defect is still to be defined.