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Mucopolysaccharidosis type IIIB may predominantly present with an attenuated clinical phenotype

Marlies J Valstar1, Hennie T Bruggenwirth, Renske Olmer

  • 1Department of Pediatrics and Amsterdam Lysosome Center Sphinx, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.

Journal of Inherited Metabolic Disease
|September 21, 2010
PubMed

Insights

Mucopolysaccharidosis type IIIB (MPS IIIB) often presents with a mild, attenuated disease course, not just the classical severe phenotype. Many patients experience slow development and live into adulthood, highlighting the need for broader diagnostic consideration.

Area of Science:

  • Biochemistry
  • Genetics
  • Pediatrics

Background:

  • Mucopolysaccharidosis type IIIB (MPS IIIB), also known as Sanfilippo syndrome type B, is a rare lysosomal storage disorder.
  • It results from a deficiency in the enzyme N-acetyl-α-D-glucosaminidase (NAGLU).
  • Limited information exists on the natural progression of MPS IIIB, which is crucial for developing new therapies.

Purpose of the Study:

  • To investigate the natural course and phenotypic spectrum of MPS IIIB.
  • To characterize the disease progression in a comprehensive cohort of Dutch patients.
  • To identify potential genotype-phenotype correlations.

Main Methods:

  • Retrospective analysis of clinical data from 44 MPS IIIB patients identified in the Netherlands.
  • Enzymatic studies for NAGLU deficiency.
  • Molecular analysis of 24 index patients.

Main Results:

  • A significant majority (79%) of patients exhibited an attenuated MPS IIIB phenotype, with slower intellectual and motor regression.
  • Only 21% presented with the classical severe MPS III phenotype.
  • Patients often showed mild developmental delay starting around age 4, followed by developmental stagnation, with many living into adulthood.
  • Specific missense mutations (p.R643C, p.S612G, p.E634K, p.L497V) were associated with the attenuated phenotype.

Conclusions:

  • MPS IIIB presents a wider spectrum of severity than previously recognized, with a predominant attenuated form.
  • The diagnosis of MPS IIIB should be considered even in cases of developmental delay without progressive intellectual decline, especially when behavioral problems are present.
  • Understanding the diverse natural history is vital for managing patients and evaluating emerging therapeutic strategies.

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