Mucopolysaccharidosis Type IIIA / Sanfilippo Syndrome A via the SGSH Gene

Summary and Pricing

Test Method

Sequencing and CNV Detection via NextGen Sequencing using PG-Select Capture Probes
Test Code Test Copy GenesTest CPT Code Gene CPT Codes Copy CPT Codes Base Price
7821 SGSH 81479 81479,81479 $640 Order Options and Pricing
Test Code Test Copy Genes Test CPT Code Gene CPT Codes Copy CPT Code Base Price
7821SGSH81479 81479(x2) $640 Order Options and Pricing

Pricing Comments

This test is also offered via our exome backbone with CNV detection (click here). The exome-based test may be higher priced, but permits reflex to the entire exome or to any other set of clinically relevant genes.

An additional 25% charge will be applied to STAT orders. STAT orders are prioritized throughout the testing process.

Turnaround Time

18 days on average for standard orders or 13 days on average for STAT orders.

Please note: Once the testing process begins, an Estimated Report Date (ERD) range will be displayed in the portal. This is the most accurate prediction of when your report will be complete and may differ from the average TAT published on our website. About 85% of our tests will be reported within or before the ERD range. We will notify you of significant delays or holds which will impact the ERD. Learn more about turnaround times here.

Targeted Testing

For ordering sequencing of targeted known variants, go to our Targeted Variants page.

EMAIL CONTACTS

Genetic Counselors

Geneticist

Clinical Features and Genetics

Clinical Features

The mucopolysaccharidoses (MPS) are a group of inherited disorders caused by defects in lysosomal enzymes responsible for the stepwise degradation of glycosaminoglycans (GAGs). Each enzyme deficiency results in progressive storage of distinct GAGs in multiple organ systems and subsequent abnormalities. Although MPS share several symptoms, including physical and mental developmental abnormalities, they may differ even within the same enzyme deficiency. Seven clinically distinct types can be recognized (Types I, II, III, IV, VI, VII, and IX). Based on the biochemical and genetic defects, MPS III and IV are further divided in four and two subtypes, respectively. Deficiencies in eleven enzymes have been implicated in the various MPS.

Mucopolysaccharidosis Type III, also known as Sanfilippo syndrome is caused by deficiency in any of four lysosomal enzymes involved in the stepwise degradation of heparan sulfate. Enzyme deficiencies result in progressive storage of heparan sulfate primarily in the central nervous system, leading to severe neurodegeneration and developmental delay. MPSIII is classified into four subtypes (MPS IIIA to D) on the basis of the specific enzyme deficiency. MPS IIIA is caused by deficiency of the heparan N-sulfatase, also designated sulfamidase.

Clinically, MPS III is distinguished from the other MPS by a severe cognitive and neurological impairment; and mild somatic signs. The characteristic features are similar in all four subtypes, although MPS IIIA is usually associated with an earlier age of onset and a faster progression compared to the other MPS. Symptoms appear during childhood and death usually occurs by the second or third decade of life. Symptoms typically begin with episodes of hyperactivity and aggressive behavior and progress to severe behavioral and sleep disturbances, speech difficulties, hearing and visual defects, and mental retardation. Somatic involvement is variable. Symptoms include mildly coarse facial features, recurrent ear and respiratory infections, scoliosis, hip dysplasia, carpal tunnel syndrome and cardiac valve disease (Neufeld and Muenzer 2001; Wijburg et al. 2013).

MPS III occurs in diverse ethnic and geographical populations with an estimated prevalence of 0.87:100,000 per live births (www.orpha.net).

Genetics

MPS IIIA is inherited in an autosomal recessive manner and is caused by pathogenic variants in the SGSH gene (Scott et al. 1995). Over 100 disease-causing variants have been reported in patients from various ethnic and geographical populations. Although most variants are missense; nonsense, splicing, small insertions or deletions and large deletions have been reported (Human Gene Mutation Database).

There are no clear genotype-phenotype correlations because most pathogenic variants are private (Yogalingam and Hopwood 2001), and because of the lack of strong correlations between specific causative mutations and residual enzyme activity (Beesley et al. 2000). In addition, modifying factors, including genetic and environmental, are suspected to contribute to the phenotypic presentation (Perkins et al. 1999).

The SGSH gene encodes for the lysosomal heparan N-sulfatase (or sulfamidase), one of four enzymes involved in the degradation of heparan sulfate.

Clinical Sensitivity - Sequencing with CNV PG-Select

Pathogenic variants were identified in over 98% of the alleles in patients diagnosed with MPS IIIA based on deficient heparan N-sulfatase activity (Valstar et al. 2010).

Although rare, large pathogenic deletions in SGSH have been reported (Ouesleti et al. 2011).

Testing Strategy

This test provides full coverage of all coding exons of the SGSH gene, plus ~10 bases of flanking noncoding DNA. We define full coverage as >20X NGS reads or Sanger sequencing.

Indications for Test

Confirmation of the diagnosis of MPS IIIA in patients with clinical features and radiological findings suggestive of MPS III, increased heparan sulfate excretion in urine, and reduced heparan N-sulfatase activity; and identification of asymptomatic heterozygous carriers.

Gene

Official Gene Symbol OMIM ID
SGSH 605270
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT

Disease

Name Inheritance OMIM ID
Mucopolysaccharidosis, MPS-III-A AR 252900

Related Test

Name
Mucopolysaccharidosis Type III Panel

Citations

  • Beesley CE, Young EP, Vellodi A, Winchester BG. 2000. Mutational analysis of Sanfilippo syndrome type A (MPS IIIA): identification of 13 novel mutations. J. Med. Genet. 37: 704–707. PubMed ID: 11182930
  • Human Gene Mutation Database (Bio-base).
  • Neufeld EF, Muenzer J. 2001. The Mucoploysaccharidoses. 136: 3421-3452.
  • Orphanet
  • Ouesleti S, Brunel V, Turkia H Ben, Dranguet H, Miled A, Miladi N, Dridi MF Ben, Lavoinne A, Saugier-Veber P, Bekri S. 2011. Molecular characterization of MPS IIIA, MPS IIIB and MPS IIIC in Tunisian patients. Clin. Chim. Acta 412: 2326–2331. PubMed ID: 21910976
  • Perkins KJ, Byers S, Yogalingam G, Weber B, Hopwood JJ. 1999. Expression and Characterization of Wild Type and Mutant Recombinant Human Sulfamidase: Implications For Sanfilippo (Mucopolysaccharidosis IIIA) Syndrome. Journal of Biological Chemistry 274: 37193–37199. PubMed ID: 10601282
  • Scott HS, Blanch L, Guo XH, Freeman C, Orsborn A, Baker E, Sutherland GR, Morris CP, Hopwood JJ. 1995. Cloning of the sulphamidase gene and identification of mutations in Sanfilippo A syndrome. Nat. Genet. 11: 465–467. PubMed ID: 7493035
  • Valstar MJ, Neijs S, Bruggenwirth HT, Olmer R, Ruijter GJG, Wevers RA, Diggelen OP van, Poorthuis BJ, Halley DJ, Wijburg FA. 2010. Mucopolysaccharidosis type IIIA: clinical spectrum and genotype-phenotype correlations. Ann. Neurol. 68: 876–887. PubMed ID: 21061399
  • Wijburg FA, Wegrzyn G, Burton BK, Tylki-Szymanska A. 2013. Mucopolysaccharidosis type III (Sanfilippo syndrome) and misdiagnosis of idiopathic developmental delay, attention deficit/hyperactivity disorder or autism spectrum disorder. Acta Paediatrica 102: 462–470. PubMed ID: 23336697
  • Yogalingam G, Hopwood JJ. 2001. Molecular genetics of mucopolysaccharidosis type IIIA and IIIB: Diagnostic, clinical, and biological implications. Hum. Mutat. 18: 264–281. PubMed ID: 11668611

Ordering/Specimens

Ordering Options

We offer several options when ordering sequencing tests. For more information on these options, see our Ordering Instructions page. To view available options, click on the Order Options button within the test description.

myPrevent - Online Ordering

  • The test can be added to your online orders in the Summary and Pricing section.
  • Once the test has been added log in to myPrevent to fill out an online requisition form.
  • PGnome sequencing panels can be ordered via the myPrevent portal only at this time.

Requisition Form

  • A completed requisition form must accompany all specimens.
  • Billing information along with specimen and shipping instructions are within the requisition form.
  • All testing must be ordered by a qualified healthcare provider.

For Requisition Forms, visit our Forms page


Specimen Types

Specimen Requirements and Shipping Details

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ORDER OPTIONS

View Ordering Instructions

1) Select Test Method (Backbone)


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2) Select Additional Test Options

STAT and Prenatal Test Options are not available with Patient Plus.

No Additional Test Options are available for this test.

Note: acceptable specimen types are whole blood and DNA from whole blood only.
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