A clinical case of rare mucopolysaccharidosis type IIIC

Abstract

Mucopolysaccharidosis type IIIC (MPS IIIC, Sanfilippo syndrome) is an inherited disease that is caused by pathogenic variants in the HGSNAT gene, which encodes the lysosomal enzyme alpha-glycosaminidase N-acetyltransferase. The characteristic phenotype is the primary indication for referral for biochemical diagnosis of accumulation diseases and subsequent molecular genetic study. The individual was observed to display delayed psychomotor development and behaviors consistent with autism spectrum disorder. Upon external examination, the subject displayed a few distinctive physical characteristics, including a coarse facial features, a dolichocephalic skull shape, stiff dark hair, thick eyebrows, a protruding lower lip, a short neck, hypertrichosis, a cylindrical chest, an umbilical hernia, long arms, and flat-valgus feet. The patient displayed a delayed psychomotor development and exhibited behaviors consistent with autism spectrum disorder. The biochemical diagnostic tests yielded results indicating an elevated total concentration of glycosaminoglycans. The results of one-dimensional electrophoresis of glycosaminoglycans demonstrated an elevated excretion of heparan sulfate in the urine. A molecular genetic study identified two pathogenic variants in the HGSNAT gene that were inherited from carrier parents. Based on the clinical data, results of biochemical and molecular genetic studies, and a comprehensive analysis, the diagnosis of ‘Mucopolysaccharidosis type IIIC’ was established. In conclusion, the case study illustrates the characteristics of MPS IIIC, including its typical phenotypic features and central nervous system involvement.