Mucopolysaccharidosis Type IIIB: NAGLU Gene Deletion/Duplication

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Condition Description

Mucopolysaccharidosis type IIIB (MPS IIIB, Sanfilippo syndrome type B), is a member of a group of inherited metabolic disorders collectively termed mucopolysaccharidoses (MPSs). The MPSs are caused by a deficiency of lysosomal enzymes required for the degradation of mucopolysaccharides or glycosaminoglycans (GAGs) within the lysosome. When functioning normally, the lysosomal enzymes break down these GAGs, however when the enzyme is deficient, the GAGs build up in the lysosomes causing damage to the bodys tissues. The MPSs share a chronic progressive course with multisystem involvement, characteristic physical features, laboratory findings, and radiographic abnormalities. MPS IIIB is an autosomal recessive caused by deficiency of the alpha-N-acetylglucosaminidase enzyme and build up of heparin sulfate.

Clinical features of MPS IIIB begin in childhood with hyperactivity, aggressiveness, and developmental delays. Mental abilities decline as the disease progresses. Involvement of other organ systems tends to be mild and dysmorphic features are more subtle than those observed in other type of mucopolysaccharidosis [1]. A small number of late onset cases have been reported.

MPS IIIB is caused by mutations in the NAGLU gene, but is clinically indistinguishable from MPS IIIA, MPS IIIC, and MPS IIID, which are caused by mutations in other genes. All four forms of MPS III result in buildup of the same GAG, heparin sulfate. Diagnostic sequencing analysis of the NAGLU gene coding region is available for MPS type IIIB patients and their at-risk relatives on a clinical basis.

For questions about testing for MPS IIIB, call the Emory Genetics Laboratory at 470-378-2200. For further clinical information about lysosomal storage diseases, including management and treatment, call the Emory Lysosomal Storage Disease Center at (404) 778-8565 or (800) 200-1524.

Visit www.ThinkGenetic.com for patient-friendly information on mucopolysaccharidosis type III.

References: 1). Muenzer, J., The mucopolysaccharidoses: a heterogeneous group of disorders with variable pediatric presentations. J Pediatr, 2004. 144(5 Suppl): p. S27-34.
2). Beesley, C.E., M. Jackson, E.P. Young, A. Vellodi, and B.G. Winchester, Molecular defects in Sanfilippo syndrome type B (mucopolysaccharidosis IIIB). J Inherit Metab Dis, 2005. 28(5): p. 759-67.
3). Beesley, C., M. Moraitou, B. Winchester, K. Schulpis, E. Dimitriou, and H. Michelakakis, Sanfilippo B syndrome: molecular defects in Greek patients. Clin Genet, 2004. 65(2): p. 143-9.
4). Tanaka, A., M. Kimura, H.T. Lan, N. Takaura, and T. Yamano, Molecular analysis of the alpha-N-acetylglucosaminidase gene in seven Japanese patients from six unrelated families with mucopolysaccharidosis IIIB (Sanfilippo type B), including two novel mutations. J Hum Genet, 2002. 47(9): p. 484-7.

Genes (1)

Indications

  • Confirmation of a clinical diagnosis of MPS IIIB
  • Prenatal testing for known familial mutations.
  • Assessment of carrier status in high risk family members - known mutation analysis.

Methodology

DNA isolated from peripheral blood is hybridized to a CGH array to detect deletions and duplications.

The targeted CGH array has overlapping probes which cover the entire genomic region.



Please note that a "backbone" of probes across the entire genome are included on the array for analytical and quality control purposes. Rarely, off-target copy number variants causative of disease may be identified that may or may not be related to the patient's phenotype. Only known pathogenic off-target copy number variants will be reported. Off-target copy number variants of unknown clinical significance will not be reported.

Detection

Detection is limited to duplications and deletions. Array CGH will not detect point mutations or intronic mutations. Results of molecular analysis must interpreted in the context of the patient's clinical and/or biochemical phenotype.

Specimen Requirements

Submit only 1 of the following specimen types

Preferred specimen type: Whole Blood

Type: Whole Blood

Specimen Requirements:

In EDTA (purple top) or ACD (yellow top) tube:
Infants (<2 years): 2-3 ml
Children (>2 years): 3-5 ml
Older Children & Adults: 5-10 ml

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.

Type: Saliva

Specimen Requirements:

OrageneTM Saliva Collection kit (available through EGL) used according to manufacturer instructions.

Specimen Collection and Shipping: Store sample at room temperature. Ship sample within 5 days of collection at room temperature with overnight delivery.

Special Instructions

Submit copies of diagnostic biochemical test results with the sample. Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed outside of Emory Genetics Laboratory, please submit a copy of the sequencing report with the test requisition. Contact the laboratory if further information is needed.

  • Mucopolysaccharide screen (urine GAG) (GA)
  • Gene Sequencing for MPS IIIA (AW) and MPS IIID (BH)
  • Known mutation analysis (Custom Diagnostics) is available to test family members.
  • Prenatal testing is available for known familial mutations only. Please call the Laboratory Genetic Counselor for specific requirements for prenatal testing before collecting a fetal sample.

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