Test ID: FXIST
X-Inactivation (XIST), Xq13.2 Deletion, FISH
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
As an aid in the diagnosis of Turner syndrome, in conjunction with CMS/8696 Chromosomes Analysis, For Congenital Disorders, Blood
To characterize marker chromosomes that are derived from the X chromosome
Genetics Test Information Provides information that may help with selection of the correct test or proper submission of the test request
Only appropriate to characterize X-derived structurally abnormal chromosomes.
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
Fluorescence In Situ Hybridization (FISH)
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Xq Deletion
Xq13.3
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Provide a reason for referral with each specimen. The laboratory will not reject testing if this information is not provided, but appropriate testing and interpretation may be compromised or delayed.
Forms:
1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (Supply T576) is available in Special Instructions.
2. If not ordering electronically, submit a Cytogenetics/AFP Congenital Disorders Request Form (Supply T238) with the specimen.
Advise Express Mail or equivalent if not on courier service.
Submit only 1 of the following specimens:
Specimen Type: Amniotic fluid
Container/Tube: Amniotic fluid container
Specimen Volume: 20-25 mL
Collection Instructions:
1. Optimal timing for specimen collection is during 14 to 18 weeks of gestation, but specimens collected at other weeks of gestation are also accepted. Provide gestational age at the time of amniocentesis.
2. Discard the first 2 mL of amniotic fluid.
Additional Information:
1. Place the tubes in a Styrofoam container (Supply T329).
2. Fill remaining space with packing material.
3. Unavoidably, about 1% to 2% of mailed-in specimens are not viable.
4. Bloody specimens are undesirable.
5. If the specimen does not grow in culture, you will be notified within 7 days of receipt.
6. Results will be reported and also telephoned or faxed, if requested.
Specimen Type: Autopsy
Container/Tube: Sterile container with sterile Hank's balanced salt solution (Supply T132), Ringer's solution, or normal saline
Specimen Volume: 4 mm diameter
Collection Instructions:
1. Wash biopsy site with an antiseptic soap.
2. Thoroughly rinse area with sterile water.
3. Do not use alcohol or iodine preparations.
4. Biopsy specimens are best taken by punch biopsy to include full thickness of dermis.
Specimen Type: Blood
Container/Tube: Green top (sodium heparin)
Specimen Volume: 5 mL
Collection Instructions:
1. Invert several times to mix blood.
2. Other anticoagulants are not recommended and are harmful to the viability of the cells.
Specimen Type: Chorionic villi
Container/Tube: 15-mL tube containing 15 mL of transport media
Specimen Volume: 20-25 mg
Collection Instructions:
1. Collect specimen by the transabdominal or transcervical method.
2. Transfer chorionic villi to Petri dish containing transport medium (Supply T095).
3. Using a stereomicroscope and sterile forceps, assess the quality and quantity of the villi and remove any blood clots and maternal decidua.
Specimen Type: Fixed cell pellet
Container/Tube: Sterile container with a 3:1 fixative (methanol:glacial acetic acid)
Specimen Volume: Entire specimen
Specimen Type: Products of conception or stillbirth
Container/Tube: Sterile container with sterile Hank's balanced salt solution (Supply T132), Ringer's solution, or normal saline
Specimen Volume: 1 cm(3) of placenta (including 20-mg of chorionic villi) and a 1-cm(3) biopsy specimen of muscle/fascia from the thigh
Collection Instructions: If a fetus cannot be specifically identified, collect villus material or tissue that appears to be of fetal origin.
Additional Information: Do not send entire fetus.
Forms: Final Disposition of Fetal/Stillborn Remains (if fetal specimen is sent) in Special Instructions
Specimen Type: Skin biopsy
Container/Tube: Sterile container with sterile Hank's balanced salt solution (Supply T132), Ringer's solution, or normal saline
Specimen Volume: 4 mm diameter
Collection Instructions:
1. Wash biopsy site with an antiseptic soap.
2. Thoroughly rinse area with sterile water.
3. Do not use alcohol or iodine preparations.
4. A local anesthetic may be used.
5. Biopsy specimens are best taken by punch biopsy to include full thickness of dermis.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | Clotted blood |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Varies | Ambient (preferred) | |
| Refrigerated | ||
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Turner syndrome is characterized by ovarian hypofunction, short stature, loose skin folds at the back of the neck, and cubitus valgus (elbow deformity) and results from complete or partial monosomy of the X chromosome.
Phenotypic expression of Turner syndrome patients is largely dependent on the patient’s karyotype and identification of sex chromosomes mosaicism plays a key role in clinical management. In mosaicism, 2 or more populations of cells with different karyotypes are present (eg, 45,X/46,XX). Additionally, mental retardation is more common in patients with a small ring chromosome derived from an X chromosome with a deletion of the X-inactivation center (XIST) at Xq13.2.
Fluorescence in situ hybridization (FISH) studies are highly specific and do not exclude other chromosome abnormalities, we recommend that patients suspected of having Turner syndrome also have conventional chromosome studies (CMS/8696 Chromosomes Analysis, for Congenital Disorders, Blood) performed to rule out other chromosome abnormalities or translocations.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
An interpretive report will be provided.
Interpretation Provides information to assist in interpretation of the test results
Any individual with a normal signal pattern (signal on each normal X homolog) in each metaphase is considered negative for a deletion in the region tested by this probe.
Any patient with a FISH signal pattern indicating loss of the XIST critical region will be reported as having a deletion of the regions by this probe.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Because this FISH test is not approved by the FDA, it is important to confirm Turner syndrome diagnoses by other established methods, such as clinical history or physical examination.
Supportive Data
FISH analysis was performed on a series of 33 patient specimens (peripheral blood or amniotic fluid) and results were compared to cytogenetic analyses and the patient's phenotype. This FISH analyses was performed on 24 samples that demonstrated a ring chromosome derived from the X chromosome. In 23 cases, XIST was present on the ring chromosome. In 1 case a deletion of XIST was identified. X chromosome rearrangements were identified in an additional 8 patients, demonstrating this probe’s ability to define other chromosome X rearrangements that are not consistent with XIST. No deletion of XIST was seen in a patient with a normal karyotype.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Van Dyke DL, Wiktor A, Palmer CG, et al: Ullrich-Turner syndrome with a small ring X chromosome and presence of mental retardation. Am J Med Genet 1992;43:996-1005
2. Sybert VP, McCauley E: Turner’s syndrome. N Engl J Med 2004;351:1227-1238
Method Description Describes how the test is performed and provides a method-specific reference
The identification of XIST deletions is based on FISH analysis of critical region loci (XIST) on the long arm of the X chromosome (Xq13.2). Metaphase cells are examined for the presence of the critical region loci at Xq13.2 (orange signal) and the control probe at the X centromere (green signal). Metaphase cells with normal X chromosomes will exhibit signals for both the critical region and control probe. Abnormal cells, those with an X-derived marker chromosome that is missing XIST, will exhibit only a control probe signal on the marker chromosome. (Crifasi PA, Michels VV, Driscoll DJ, et al: DNA fluorescent probes for diagnosis of velocardiofacial and related syndromes. Mayo Clin Proc 1995;195[70]:1148-1153)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Samples processed Monday through Sunday. Results reported Monday through Friday, 8 a.m.-5 p.m. CST.
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
88271 x 2-DNA probe, each
88273-Chromosomal in situ hybridization
88291-Interpretation and report
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 23193 | Specimen | 31208-2 |
| 23194 | Specimen ID | N/A |
| CG279 | Source | N/A |
| 23196 | Order Date | N/A |
| CG281 | Reason For Referral | 42349-1 |
| 23198 | Method | In Process |
| 23199 | Result | In Process |
| 23200 | Interpretation | 69965-2 |
| 23201 | Amendment | In Process |
| 23202 | Consultant | N/A |
| 23203 | Released Date | N/A |
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