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

Within 10 days

New York DOH Approval Status
This test is New York DOH approved.
Specimen Required
Patient Preparation
Collect

Fetal Specimen: Amniotic fluid or two T-25 flasks at 80 percent confluency of cultured amniocytes. If the client is unable to culture amniocytes, this can be arranged by contacting ARUP Client Services at (800) 522-2787.
AND Maternal Specimen
: Lavender (EDTA), pink (K2EDTA), or yellow (ACD Solution A or B).

Specimen Preparation

Amniotic Fluid: Transport 10 mL unspun fluid. (Min: 5 mL)
Cultured Amniocytes:
Fill flasks with culture media. Transport two T-25 flasks at 80 percent confluency of cultured amniocytes. Backup cultures must be retained at the client's institution until testing is complete.
Maternal Specimen:
Transport 3 mL whole blood. (Min: 1 mL)

Storage/Transport Temperature

Amniotic Fluid: Room temperature.
Cultured Amniocytes:
CRITICAL ROOM TEMPERATURE. Must be received within 48 hours of shipment due to viability of cells.
Maternal Specimen:
Room temperature.

Unacceptable Conditions
Remarks

Maternal specimen is recommended for proper test interpretation. Order Maternal Cell Contamination, Maternal Specimen. This can be arranged by contacting ARUP genetic counselors at (800) 242-2787 ext. 2141. Patient History Form is available on the ARUP Web site or by contacting ARUP Client Services at (800) 522-2787.

Stability

Fetal Specimen: Ambient: 48 hours; Refrigerated: Unacceptable; Frozen: Unacceptable
Maternal Specimen
: Ambient: 1 week; Refrigerated: 1 month; Frozen: 6 months

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.

For quality assurance purposes, ARUP Laboratories will confirm the above result at no charge following delivery. Order Confirmation of Fetal Testing and include a copy of the original fetal report (or the mother's name and date of birth) with the test submission. Please contact an ARUP genetic counselor at (800) 242-2787 extension 2141 prior to specimen submission.


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
N/A
CPT Codes

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

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 31208-2
0051389 Fragile X Fetal Specimen
2010041 Fragile X Interpretation, Fetal
* 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