Prenatal test for fetuses of mothers with fragile X premutations or full mutations.
- Patient Preparation
- 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
- 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.
- Fetal Specimen: Ambient: 48 hours; Refrigerated: Unacceptable; Frozen: Unacceptable
Maternal Specimen: Ambient: 1 week; Refrigerated: 1 month; Frozen: 6 months
Characteristics: Fragile X syndrome, the most common heritable form of mental retardation, is characterized by moderate mental retardation in males and mild mental retardation in females, hyperactivity, perseverative speech, social anxiety, poor eye contact, hand flapping or biting, autism spectrum disorders behavioral phenotype, and connective tissue anomalies. Adult males may have physical findings including: macroorchidism, a long narrow face, prominent ears and jaw, and a single palmar crease.
Incidence: 1 in 4,000 Caucasian males and 1 in 8,000 Caucasian females; unknown in other ethnicities
Inheritance: X-linked dominant.
Penetrance: Reduced in females.
Cause: Expansion of the FMR1 gene CGG triplet repeat.
Full mutation: >200-230 CGG repeats (methylated)
Premutation: 55-200 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. Methylation analysis is used to distinguish between premutation and full mutation alleles.
Analytic Sensitivity and Specificity: 99 percent
Limitations: Diagnostic errors can occur due to rare sequence variations.
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|
Counseling and informed consent are recommended for genetic testing. Consent forms are available online.
|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|
- 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)