Abstract

Sanfilippo syndrome type B (Mucopolysaccharidosis IIIB) is a lysosomal storage disease resulting from deficiency of N-acetyl-glucosaminidase activity. A 12-month-old Saudi boy was presented to outpatient department in Assir Central Hospital, Saudi Arabia, with history of regression of milestone. Sanfilippo syndrome is a rare genetic disorder and can be missed easily during the routine health visit and it should be considered in the differential diagnosis of developmental delay or milestone regression and hence considering the subsequent investigation.