Mucopolysaccharidosis type III (subtype IIIB) diagnosis as a spectrum disorder: A case report from Kosovo

Mucopolysaccharidosis type IIIB (MPS IIIB), also known as Sanfilippo syndrome type B, is a metabolic disease caused by mutations in both alleles of the NAGLU gene encoding for the enzyme α-N-acetylglucosaminidase. A malfunction of this enzyme causes  inability to degrade heparan sulfate, which leads to accumulation of glycosaminoglycans in the cells. MPS IIIB is associated with different symptoms such as neurodegeneration, extreme hyperactivity, sleeping problems, aggressive behavior, reduced fear, and cognitive  deterioration. The condition is by now not curable. Here we describe a patient with MPS IIIB diagnosed at the age of 5 presenting with communication problems, motor dysfunctions, and speech and sleeping problems.Standard biochemical tests for neurodegenerative disorders and DNA analyses including NAGLU mutation screening were performed. We also did some psychological tests assessing the patient's communication skills and behavior. The patient was heterozygote for two mutations in the gene NAGLU (Y140C and Ser169fs). Thus, he suffered from MPS IIIB due to two mutations in the disease-causing gene.The patient presented with clear signs and symptoms of MPS IIIB with at least one of the two mutations affecting the α-N-acetylglucosaminidase protein function severely. Here we report the combination of a well-known and previously unreported mutation in the NAGLU gene; this could be dependent on geographical origin of the patient, which needs to be clarified by molecular studies of more MPS IIIB patients from Southeast Europe.