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Thrombocytopenia Absent Radius (TAR) Syndrome via the RBM8A 1q21.1 Deletion

Summary and Pricing

Test Method

Whole-Genome Chromosomal Microarray (CMA-ISCA) via aCGH/SNP
Test Code Test Copy GenesTest CPT Code Gene CPT Codes Copy CPT Codes Base Price
RBM8A 81479 81479 $750
Test Code Test Copy Genes Test CPT Code Gene CPT Codes Copy CPT Code Base Price
1718RBM8A81479 81479 $750 Order Options and Pricing

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

Turnaround Time

The great majority of tests are completed within 3 weeks (abnormal findings are typically issued in preliminary report). Cases requiring confirmatory tests will delay issue of final report.

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.


Genetic Counselors


  • Siwu Peng, PhD

Clinical Features and Genetics

Clinical Features

Thrombocytopenia with Absent Radius Syndrome (TAR) (CTRUS) is characterized by thrombocytopenia, bleeding diathesis, and absence of the radius with preservation of the thumb. Bleeding episodes associated with TAR tend to be moderate to severe after birth, but tend to diminish in frequency and severity over time. Skeletal abnormalities may extend to the absence of upper limbs and to the hips and knees (Greenhalgh et al. 2002). Absent radius combined with a blood phenotype is also a characteristic of Fanconi anemia (FA); FA can be distinguished from TAR by absence of the thumb in addition to the absent radius (Tischkowitz and Hodgson 2003; Dokal 2000). Other symptoms of TAR may include intolerance to cow’s milk, renal anomalies, and cardiac anomalies (Greenhalgh et al. 2002).


TAR does not appear to follow a typical autosomal dominant or recessive pattern of inheritance. Rather, the vast majority of patients with TAR have a compound inheritance that includes a null allele and a low frequency variant in the RBM8A gene. Most patients with TAR harbor a large deletion of chromosome 1q21.1, which includes the RBM8A gene (Klopocki et al. 2007; Papoulidis et al. 2014). Other reported null variants associated with TAR include a small insertion (c.207_208insAGCG) resulting in premature protein termination (p.Val70Serfs*3) (Albers et al. 2012) and a nonsense variant c.487C>T (p.Arg163*) (Albers et al. 2012). Paring one of these null alleles with one of two noncoding variants on the other allele, either c.-21G>A or c.67+32G>C, is strongly associated with disease; this combination of variants was found in 53 of 55 cases in one report with 51 cases having a large 1q21.1 deletion (Albers et al. 2012). This test involves testing for the large 1q21.1 deletion found in many TAR patients.

Due to the high frequency of a combination of the large 1q21.1 deletion and a sequence variant in patients with TAR, we also offer a separate comprehensive RBM8A sequencing PLUS deletion test and an individual RBM8A gene sequencing test.

Clinical Sensitivity - CMA

In one study, 51 of 55 cases, or approximately 93% of TAR syndrome patients, were found to harbor one of two "functional polymorphisms" in the RBM8A gene (either c.-21G>A or c.67+32G>C) in combination with a large 1q21.1 deletion that includes the RBM8A gene (Albers et al 2012). An additional 2 patients were found to harbor one of the two functional polymorphisms in combination with a null allele other than the large 1q21.1 deletion.   

Testing Strategy

Testing for the 1q21.1 deletion includes analysis of only the RBM8A gene using our high density chromosomal microarray (CMA).

Testing for sequence variants in the RBM8A gene and for the large 1q21.1 deletion is recommended if the index of suspicion for TAR is high.

Indications for Test

This test is indicated for patients with absent radius with or without thrombocytopenia and patients with absent radius with other symptoms such as intolerance to cow's milk, cardiac anomalies, and renal anomalies. This test is also recommended for patients with suspected TAR who were found to harbor a plausible pathogenic sequence variant, such as c.-21G>A or c.67+32G>C, in the RBM8A gene through sequencing.


Official Gene Symbol OMIM ID
RBM8A 605313
Inheritance Abbreviation
Autosomal Dominant AD
Autosomal Recessive AR
X-Linked XL
Mitochondrial MT


Name Inheritance OMIM ID
Thrombocytopenia-Absent Radius Syndrome AR 274000

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Thrombocytopenia Absent Radius (TAR) Syndrome via the RBM8A Gene
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  • Albers C.A. et al. 2012. Nature Genetics. 44: 435-9, S1-2. PubMed ID: 22366785
  • Dokal I. 2000. The genetics of Fanconi’s anaemia. Baillieres Best Pract. Res. Clin. Haematol. 13: 407–425. PubMed ID: 11030042
  • Greenhalgh K.L. et al. 2002. Journal of Medical Genetics. 39: 876-81. PubMed ID: 12471199
  • Klopocki E. et al. 2007. American Journal of Human Genetics. 80: 232-40. PubMed ID: 17236129
  • Papoulidis I. et al. 2014. Molecular Medicine Reports. 9: 163-5. PubMed ID: 24220582
  • Tischkowitz M.D., Hodgson S.V. 2003. Journal of Medical Genetics. 40: 1-10. PubMed ID: 12525534


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