Sanfilippo type D presenting with acquired language disorder but without features of mucopolysaccharidosis

A 7-year-old girl presented with a language disorder reminiscent of verbal auditory agnosia. Later, she proved to have defective N-acetylglucosamine-6-sulfate sulfatase, the enzyme deficient in Sanfilippo D syndrome. She did not show clinical features of mucopolysaccharidosis. The language disorder had a fluctuating course, which eventually evolved into a progressive dementing encephalopathy.