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Test Code FXS Fragile X Syndrome, Molecular Analysis, Varies

Useful For

Confirmation of a diagnosis of fragile X syndrome, fragile X tremor/ataxia syndrome, or premature ovarian insufficiency caused by expansions in the FMR1 gene


Determination of carrier status for individuals with a family history of fragile X syndrome or X-linked intellectual disability


Prenatal diagnosis of fragile X syndrome when there is a documented FMR1 expansion in the family

Reflex Tests

Test ID Reporting Name Available Separately Always Performed
CULFB Fibroblast Culture for Genetic Test Yes No
CULAF Amniotic Fluid Culture/Genetic Test Yes No
MATCC Maternal Cell Contamination, B Yes No
FUFXS Fragile X, Follow up Analysis No No

Testing Algorithm

When this test is ordered, fragile X follow-up analysis testing will be performed and charged dependent upon the reported gender of the individual and on the size of the CGG repeat found by PCR analysis.


When sending in prenatal specimens: If amniotic fluid (nonconfluent cultured cells) is received, amniotic fluid culture/genetic test will be added and charged separately. If chorionic villus specimen (nonconfluent cultured cells) is received, fibroblast culture for genetic test will be added and charged separately. For any prenatal specimen that is received, maternal cell contamination studies will be added.

Method Name

Polymerase Chain Reaction (PCR)-Based Assays

Reporting Name

Fragile X Syndrome, Mol. Analysis

Specimen Type


Advisory Information

Due to the complexity of prenatal testing, consultation with the laboratory is required for all prenatal testing.


FMR1-methylation status cannot be assessed on chorionic villus specimens. Contact a molecular genetic counselor/consultant at 800-533-1710 to discuss the limitations of testing prior to sending a chorionic villus specimen for fragile X analysis.

Additional Testing Requirements

All prenatal specimens must be accompanied by a maternal blood specimen. Order MATCC / Maternal Cell Contamination, Molecular Analysis on the maternal specimen.

Shipping Instructions

Specimen preferred to arrive within 96 hours of collection.


Prenatal specimens can be sent Monday through Thursday and must be received by 5 p.m. CST on Friday in order to be processed appropriately.

Specimen Required

Patient Preparation: A previous bone marrow transplant from an allogenic donor will interfere with testing. Call 800-533-1710 for instructions for testing patients who have received a bone marrow transplant.


Submit only 1 of the following specimens:


Specimen Type: Whole blood


Preferred: Lavender top (EDTA) or yellow top (ACD)

Acceptable: Any anticoagulant

Specimen Volume: 3 mL

Collection Instructions:

1. Invert several times to mix blood.

2. Send specimen in original tube.

Specimen Stability Information: Ambient (preferred)/Refrigerated


Prenatal Specimens


Specimen Type: Amniotic fluid

Container/Tube: Amniotic fluid container

Specimen Volume: 20 mL

Specimen Stability Information: Refrigerated (preferred)/Ambient


Specimen Type: Chorionic villi

Container/Tube: 15-mL tube containing 15 mL of transport media

Specimen Volume: 20 mg

Specimen Stability Information: Refrigerated



Specimen Type: Confluent cultured cells

Container/Tube: T-25 flask

Specimen Volume: 2 flasks

Collection Instructions: Submit confluent cultured cells from another laboratory.

Specimen Stability Information: Ambient (preferred)/Refrigerated

Specimen Minimum Volume

Blood: 0.5 mL
Amniotic Fluid: 10 mL
Chorionic Villi: 5 mg

Specimen Stability Information

Specimen Type Temperature Time Special Container
Varies Varies

Reject Due To

Specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Reference Values

Normal alleles: 5-44 CGG repeats

Intermediate (grey zone) alleles: 45-54 CGG repeats

Premutation alleles: 55-200 CGG repeats

Full mutation alleles: >200 CGG repeats

An interpretive report will be provided.


Methylation status:

Unmethylated: ≤20%

Partially methylated: 21-69%

Fully methylated: ≥70%

Day(s) and Time(s) Performed

Monday, Wednesday; 10 a.m.

Performing Laboratory

Mayo Clinic Laboratories in Rochester

CPT Code Information


88233-(if appropriate)

88240-(if appropriate)

88235-(if appropriate)

88240-(if appropriate)

81265-(if appropriate)

81244-(if appropriate)

LOINC Code Information

Test ID Test Order Name Order LOINC Value
FXS Fragile X Syndrome, Mol. Analysis In Process


Result ID Test Result Name Result LOINC Value
52870 Result Summary 50397-9
52871 Result 81856-7
52872 Interpretation 69047-9
52873 Reason for Referral 42349-1
52874 Specimen 31208-2
52875 Source 31208-2
52876 Method 49549-9
52877 Released By 18771-6

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.


1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Molecular Genetics: Congenital Inherited Diseases Patient Information (T521) in Special Instructions

3. If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.