Mucopolysaccharidosis type IIIC diagnosed at the age of 12 years: Why was the disease diagnosed so late?

Mucopolysaccharidoses (MPS) are a group of inherited metabolic diseases associated with impaired lysosomal degradation of glycosaminoglycans. The aim of this manuscript is to report a case of a patient with mucopolysaccharidosis type IIIC (MPS IIIC) diagnosed at 12 years of age - to raise awareness among pediatricians, pediatric neurologists, and endocrinologists about the possible misdiagnosis. The patient was initially diagnosed with autism spectrum disorder and hyperactivity with normal motor development. During follow-up, psychomotor regression with moderate intellectual disability was observed. The patient was referred for further metabolic work-up only after the results of molecular analysis suggesting MPS IIIC. The final diagnosis was established based on clinical, biochemical, and molecular analyses.