Sialidosis type 2 in Japan. Clinical study in two siblings' cases and review of literature.

Clinical and biochemical findings in two siblings (24-year-old sister and 20-year-old brother), born to consanguineous parents, are described. Both showed progressive generalized myoclonus, macular cherry-red spots, moderate cerebellar ataxia, coarse facies, vertebral deformities, vacuolation of peripheral lymphocytes, bone marrow cells and epithelial cells of conjunctiva, but had normal intelligence. The excretion of sialyloligosaccharides in the urine of both was 3-5 times larger than in the controls. The activities of alpha-neuraminidase and beta-galactosidase in leukocytes and cultured skin fibroblasts were reduced. The clinical and biochemical findings were those of the newly described condition, sialidosis type 2. Review of all Japanese cases considered as sialidosis type 2 showed that the most characteristic clinical features as distinct from type 1, were coarse facies and bone deformities, especially of vertebral bodies.