Mucopolysaccharidosis III B: hybridization studies on fibroblasts from a mild case and fibroblasts from severe patients.

Cell fusion with polyethylene glycol (PEG) was performed on fibroblasts from a previously studied patient with a mild form of Sanfilippo B disease and altered residual enzyme activity and fibroblasts from several patients with the classical, severe form of the disease. No complementation was found in heterokaryons. This suggests that the mild phenotype in our patient can be ascribed to an allelic mutation.