Fragile X (FMR1) with Reflex to Methylation Analysis, Fetal

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Additional Technical Information

Ordering Recommendation

Prenatal test for fetuses of mothers with fragile X premutations or full mutations.

Mnemonic

FX PCR FE

Methodology

Polymerase Chain Reaction/Capillary Electrophoresis

Performed

Sun-Sat

Reported

10 days; if culture is required, an additional 1 to 2 weeks is required for processing time.

New York DOH Approval Status

This test is New York DOH approved.

Specimen Required

Patient Preparation
Collect

Fetal Cultured Amniocytes or Cultured CVS
AND Maternal Whole Blood Specimen: Lavender (EDTA), pink (K 2 EDTA), or yellow (ACD Solution A or B).

Specimen Preparation

Cultured Amniocytes or Cultured CVS: Transfer cultured amniocytes or cultured CVS to two T-25 flasks at 80 percent confluence (Min: one T-25 flask at 80 percent confluence). Backup cultures must be retained at the client's institution until testing is complete. If ARUP receives a sample below the minimum confluence, CG GRW&SND (0040182) will be added on by ARUP, and additional charges will apply. If clients are unable to culture specimens, CG GRW&SND should be added to initial order.
Maternal Whole Blood Specimen: Transport 2 mL whole blood. (Min: 1 mL)

Storage/Transport Temperature

Cultured Amniocytes or Cultured CVS: CRITICAL ROOM TEMPERATURE. Must be received within 48 hours of collection due to viability of cells.
Maternal Whole Blood Specimen: Room temperature.

Unacceptable Conditions
Remarks
Stability

Cultured Amniocytes or Cultured CVS: Room temperature: 48 hours; Refrigerated: Unacceptable; Frozen: Unacceptable
Maternal Whole Blood Specimen: Room temperature: 7 days; Refrigerated: 1 month; Frozen: Unacceptable

Reference Interval

By report

Interpretive Data

Background information for Fragile X (FMR1) with Reflex to Methylation Analysis, Fetal
Characteristics of Fragile X syndrome (FXS): Affected males have moderate intellectual disability, hyperactivity, perseverative speech, social anxiety, poor eye contact, hand flapping or biting, autism spectrum disorders and connective tissue anomalies in males. Females are usually less severely affected than males.
Characteristics of Fragile X Tremor Ataxia Syndrome (FXTAS): Onset of progressive ataxia and intention tremor typically after the fourth decade of life. Females also have a 21 percent risk for primary ovarian insufficiency. Incidence of FXS: 1 in 4,000 Caucasian males and 1 in 8,000 Caucasian females.
Inheritance: X-linked.
Penetrance of FXS: Complete in males; 50 percent in females.
Penetrance of FXTAS: 47 percent in males and 17 percent in females >50 years of age.
Cause: Expansion of the FMR1 gene CGG triplet repeat.
Full mutation: typically >200 CGG repeats (methylated).
Premutation: 55 to approx 200 CGG repeats (unmethylated).
Intermediate: 45-54 CGG repeats (unmethylated).
Normal: 5-44 CGG repeats (unmethylated).
Clinical Sensitivity: 99 percent.
Methodology: Triplet repeat-primed polymerase chain reaction (PCR) followed by size analysis using capillary electrophoresis. Methylation-specific PCR analysis is performed for CGG repeat lengths of 55 or greater to distinguish between premutation and full mutation alleles.
Analytic Sensitivity and Specificity: 99 percent; estimated precision of sizing for intermediate and premutation alleles is within 2-3 CGG repeats.
Limitations: Methylation patterns may not be fully established in early gestation; thus, diagnostic testing on chorionic villus samples is not recommended. Diagnostic errors can occur due to rare sequence variations. Rare FMR1 variants unrelated to trinucleotide expansion will not be detected. A specific CGG repeat size estimate is not provided for full mutation alleles. AGG trinucleotide interruptions within the FMR1 CGG repeat tract are not assessed.

This test was developed and its performance characteristics determined by ARUP Laboratories. It has not been cleared or approved by the US Food and Drug Administration. This test was performed in a CLIA certified laboratory and is intended for clinical purposes.

Counseling and informed consent are recommended for genetic testing. Consent forms are available online.


Phenotype Number of CGG Repeats
Unaffected < 45
Intermediate 45-54
Premutation 55-200
Affected >200

Compliance Category

Laboratory Developed Test (LDT)

Note

If a CGG repeat of 100 or greater is detected by PCR and Capillary Electrophoresis; methylation analysis will be added. Additional charges apply.

Hotline History

View Hotline History

 

Hotline History

Date of Change
Test Name Change
Methodology
Performance/Reported Schedule
Specimen Requirements
Reference Interval
Interpretive Data
Note
CPT Code
Component Change
Other Interface Change
New Test
Inactive
09/07/2021
X
N/A

CPT Codes

81243; 81265 Fetal Cell Contamination (FCC); if reflexed, add 81244

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Components

Component Test Code* Component Chart Name LOINC
0050548 Maternal Contamination Study Fetal Spec 59266-7
0050556 Fragile X Allele 1 45321-7
0050558 Fragile X Allele 2 45322-5
0050559 Fragile X Methylation Pattern 41107-4
0050612 Maternal Contam Study, Maternal Spec 66746-9
0051389 Fragile X Fetal Specimen 66746-9
2010041 Fragile X Interpretation, Fetal 36914-0
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.

Aliases

  • Cytogenetics, High Resolution & Fragile X DNA (Fragile X (FMR1) Diagnostic, Fetal)
  • High Resolution & Fragile X DNA (Fragile X (FMR1) Diagnostic, Fetal)
  • Inherited Mental Retardation (Fragile X (FMR1) Diagnostic, Fetal)
  • Martin-Bell Syndrome (Fragile X (FMR1) Diagnostic, Fetal)
Fragile X (FMR1) with Reflex to Methylation Analysis, Fetal