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Sitosterolemia via the ABCG8 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
15221 ABCG8 81479 81479,81479 $640 Order Options and Pricing
Test Code Test Copy Genes Test CPT Code Gene CPT Codes Copy CPT Code Base Price
15221ABCG881479 81479,81479 $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

  • Luke Drury, PhD

Clinical Features and Genetics

Clinical Features

Sitosterolemia is a disorder hallmarked by a 30-100 fold increase in plasma plant sterols. Heightened levels are due to defects in the adenosine triphosphate-binding cassette transporter protein which effluxes free sterols from hepatocytes and enterocytes into the gut lumen. The primary clinical features of sitosterolemia patients are tendon or tuberous xanthomas and accelerated atherosclerosis which have been report in individuals as young as 4 years of age (Mymin et al. 2003). Hemolytic anemia, stomatocyte formation, and macrothrombocytopenia are common hematologic findings and may be the only clinically observed symptoms in patients (Wang et al. 2014; Escolá-Gil et al. 2014). Clinical colormetric enzyme assays to quantify sterols cannot discriminate between cholesterol and plant sterols making diagnosis difficult (Kidambi and Patel 2008). Genetic testing is helpful in the differential diagnosis of sitosterolemia from cerebrotendinous xanthomatosis, cardiovascular disease, and familial hypercholesterolemia. Ezetimibe, an inhibitor of intestinal cholesterol absorption, has been shown to be effective in reducing plasma sterol levels (Othman et al. 2015).

Genetics

Sitosterolemia is inherited in an autosomal recessive manner with mutations in the ABCG5 and ABCG8 genes being responsible for 1/3 and 2/3 of cases respectively (Lee et al 2001; Escolá-Gil et al. 2014; Hubacek et al. 2001). The ABCG5 and ABCG8 genes encode the heterodimer adenosine triphosphate-binding cassette transporter protein present on enterocytes and hepatocytes. In enterocytes, the transporter is located on the apical membrane and promotes efflux of plant sterols back into the intestinal lumen. In the liver, the transporter is responsible for excretion of plant sterols into the bile (Lee et al. 2001). Pathogenic variants in the ABCG5 and ABCG8 genes impair transporter function or surface expression and result in elevated plasma plant sterol levels.

The c.1083G>A (previously reported as c.1173G>A) variant resulting in a nonsense change (p.Trp361*) accounts for half of all pathogenic alleles in the ABCG8 gene (Lu et al. 2001). Loss of function variants represent over two-thirds of the documented mutations and include nonsense, frameshift, and splice site alterations found throughout the gene. Missense variants represent about a third of cases, and no gross deletions have been reported (Lu et al. 2001; Escolá-Gil et al. 2014). Pathogenic variants in the in the ABCG8 gene are more commonly found in Caucasian populations (Kidambi and Patel 2008).

Clinical Sensitivity - Sequencing with CNV PG-Select

To date, only about 100 cases of sitosterolemia have been reported (Escolá-Gil et al. 2014). In a series of 25 unrelated families with a diagnosis of sitosterolemia based on elevated plasma sitosterol levels, pathogenic variants in the ABCG5 and ABCG8 genes were found in 9 of 25 and 16 of 25 families respectively (Lu et al. 2001). Analytical sensitivity for detection of pathogenic variants in the ABCG5 and ABCG8 genes is >95%. Two cases of a deletion of exon 3 in the ABCG5 gene have been reported and are not predicted to be detected by this sequencing method (Lu et al. 2001).

Testing Strategy

This test is performed using Next-Generation sequencing with additional Sanger sequencing as necessary.

This test provides full coverage of all coding exons of the ABCG8 gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing.

Indications for Test

Candidates for testing include patients presenting with xanthomas, premature atherosclerosis, hemolytic anemia, and macrothrombocytopenia. Presence of stomatocytes in bloods smears and elevated plant sterol levels (>20-30mg/dl) are common laboratory findings. Gas chromatography or high performance liquid chromatography are necessary to specifically measure plant sterol levels as colormetric assays to measure sterols do not differentiate between cholesterol and plant sterols (Kidambi and Patel 2008; Lu et al. 2001). This test may also be considered for the reproductive partners of individuals who carry pathogenic variants in ABCG8.

Gene

Official Gene Symbol OMIM ID
ABCG8 605460
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT

Disease

Name Inheritance OMIM ID
Sitosterolemia AR 210250

Citations

  • Escol√†-Gil J.C. et al. 2014. Current Atherosclerosis Reports. 16: 424. PubMed ID: 24821603
  • Hubacek J.A. et al. 2001. Human Mutation. 18: 359-60. PubMed ID: 11668628
  • Kidambi S., Patel S.B. 2008. Journal of Clinical Pathology. 61: 588-94. PubMed ID: 18441155
  • Lee M.H. et al. 2001. Nature Genetics. 27: 79-83. PubMed ID: 11138003
  • Lu K. et al. 2001. American Journal of Human Genetics. 69: 278-90. PubMed ID: 11452359
  • Mymin D. et al. 2003. Circulation. 107: 791. PubMed ID: 12578886
  • Othman R.A. et al. 2015. The Journal of Pediatrics. 166: 125-31. PubMed ID: 25444527
  • Wang Z. et al. 2014. American Journal of Hematology. 89: 320-4.¬† PubMed ID: 24166850

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)


1) Select Test Type


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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