Sanfilippo syndrome type B: Analysis of patients diagnosed by the MPS Brazil Network

Mucopolysaccharidosis type IIIB is a rare autosomal recessive disorder characterized by deficiency of the enzyme N-acetyl-alpha-d-glucosaminidase (NAGLU), caused by biallelic pathogenic variants in the NAGLU gene, which leads to storage of heparan sulfate and a series of clinical consequences which hallmark is neurodegeneration. In this study clinical, epidemiological, and biochemical data were obtained from MPS IIIB patients diagnosed from 2004-2019 by the MPS Brazil Network ("Rede MPS Brasil"), which was created with the goal to provide an easily accessible and comprehensive investigation of all MPS types. One hundred and ten MPS IIIB patients were diagnosed during this period. Mean age at diagnosis was 10.9 years. Patients were from all over Brazil, with a few from abroad, with a possible cluster of MPS IIIB identified in Ecuador. All patients had increased urinary levels of glycosaminoglycans and low NAGLU activity in blood. Main clinical symptoms reported at diagnosis were coarse facies and neurocognitive regression. The most common variant was p.Leu496Pro (30% of alleles). MPS IIIB seems to be relatively frequent in Brazil, but patients are diagnosed later than in other countries, and reasons for that probably include the limited awareness about the disease by health professionals and the difficulties to access diagnostic tests, factors that the MPS Brazil Network is trying to mitigate.