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.