An Uncommon Presentation of Mucopolysaccharidosis Type IIIb.

Mucopolysaccharidosis type III (MPS III; Sanfilippo syndrome) is a metabolic disorder characterized by a lysosomal enzyme deficiency in the catabolic pathway of heparan sulfate. The patients with mucopolysaccharidosis type III usually present with declined neurocognitive functions such as speech and hearing loss. Subtle somatic features of patients with mucopolysaccharidosis type III can lead to diagnostic delay and consequently, a greater neurocognitive deterioration may happen. Herein, we report a 9-yr-old boy referred to Loghman Hospital, Tehran, Iran, in 2018. He had developed normally up to four yr of age when his symptoms initiated with behavioral disturbances such as auditory agnosia and decreased verbal communication. Progression of his symptoms to seizure and ataxia, brain perfusion scan and electroencephalography features strongly suggested landau-Kleffner syndrome. However, results of gene sequencing analysis and high urinary glycosaminoglycan excretion confirmed mucopolysaccharidosis type III as his final diagnosis. This case strongly recommends screening for metabolic disorders such as mucopolysaccharidosis type III in the patients diagnosed as having landau-Kleffner syndrome.