Fragile X Syndrome, Diagnostic

CPT: 81243; 81244

Synonyms

  • Fragile X Testing
  • Fragile X-associated primary ovarian insufficiency (FXPOI)
  • Fragile X-associated tremor and ataxia syndrome (FXTAS)

Special Instructions

To test fetal specimens, including cord blood, order Fragile X Syndrome, Fetal Analysis [481718].


Expected Turnaround Time

8 - 14 days. In some cases, additional time may be required for confirmatory or reflex tests.


Specimen Requirements


Specimen

Whole blood or PurFlock buccal swab kit or Oragene Dx saliva kit


Volume

8.5 mL whole blood or PurFlock buccal swab kit or Oragene Dx saliva kit


Minimum Volume

3 mL whole blood or PurFlock buccal swab kit or Oragene Dx saliva kit


Container

Yellow-top (ACD-A), lavender-top (EDTA), pink-top (EDTA) or tan-top (EDTA) tubes, or PurFlock buccal swab kit or Oragene Dx 500 saliva collection kit


Collection

Standard phlebotomy. Follow PurFlock buccal swab kit or Oragene Dx 500 saliva kit collection instructions. Do not eat, drink, smoke or chew gum 30 minutes prior to collection.


Storage Instructions

Maintain specimen at room temperature or refrigerate at 4°C. Do not freeze.


Stability Requirements

Whole blood: 14 days at room temperature or 30 days at 4°C

Buccal: 60 days at room temperature

Saliva: 60 days at room temperature


Causes for Rejection

Frozen or hemolyzed specimen; quantity not sufficient for analysis; improper container


Test Details


Use

This test is used for diagnostic testing for unexplained intellectual disabilities, developmental delay, or autism; women with primary ovarian insufficiency or failure, premature menopause, or infertility associated with elevated FSH levels before the age of 40 with no known cause; individuals with late onset intention tremor and/or cerebellar ataxia of unknown origin; and FMR1.


Limitations

Technologies used do not detect germline mosaicism and do not rule out the presence of large chromosomal aberrations including rearrangements and gene fusions, or variants in regions or genes not included in this test, or possible inter/intragenic interactions between variants, or repeat expansions. Variant classification and/or interpretation may change with time if more information becomes available. False positive or false negative results may occur for reasons that include: rare genetic variants, sex chromosome abnormalities, pseudogene interference, blood transfusions, bone marrow transplantation, somatic or tissue-specific mosaicism, mislabeled samples or erroneous representation of family relationships. This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.


Methodology

Polymerase chain reaction (PCR) followed by capillary electrophoresis, methylation PCR analysis and reflex to AGG interruption analysis when appropriate


References

Hunter JE, Berry-Kravis H, Hipp H, et al, editors. In: GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993. 1998 Jun 16 [updated 2019 Nov 21].20301558
Spector E, Behlmann A, Kronquist K, et al. Laboratory testing for fragile X, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG). Genet Med. 2021 May;23(5):799-812.33795824

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