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HelpTest ID WS7F Williams Syndrome, 7q11.23 Deletion, FISH
Useful For
Establishing a diagnosis of Williams syndrome
Detecting cryptic rearrangements involving 7q11.23 that are not demonstrated by conventional chromosome studies
Reflex Tests
| Test ID | Reporting Name | Available Separately | Always Performed |
|---|---|---|---|
| _PBCT | Probe, +2 | No, (Bill Only) | No |
| _PADD | Probe, +1 | No, (Bill Only) | No |
| _PB02 | Probe, +2 | No, (Bill Only) | No |
| _PB03 | Probe, +3 | No, (Bill Only) | No |
| _ML10 | Metaphases, 1-9 | No, (Bill Only) | No |
| _M30 | Metaphases, ≥10 | No, (Bill Only) | No |
| _IL25 | Interphases, <25 | No, (Bill Only) | No |
| _I099 | Interphases, 25-99 | No, (Bill Only) | No |
| _I300 | Interphases, ≥100 | No, (Bill Only) | No |
Testing Algorithm
This test includes a charge for application of the first probe set (2 FISH probes) and professional interpretation of results. Additional charges will be incurred for all reflex probes performed. Analysis charges will be incurred based on the number of cells analyzed per probe set. If no cells are available for analysis, no analysis charges will be incurred.
Special Instructions
Method Name
Fluorescence In Situ Hybridization (FISH)
Reporting Name
Williams Syn, 7q11.23 Del, FISHSpecimen Type
VariesProvide 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: 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.
Advise Express Mail or equivalent if not on courier service.
Submit only 1 of the following specimens:
Preferred:
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.
Acceptable:
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: Chorionic villi
Container/Tube: 15-mL tube containing 15 mL of transport medium
Specimen Volume: 20-30 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: 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
Amniotic Fluid: 5 mL/Blood: 2 mL/Chorionic Villi: 5 mg
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Varies | Refrigerated (preferred) | |
| Ambient | ||
Clinical Information
Williams syndrome (WS) is a genetic disorder that occurs in 1/20,000 to 1/50,000 live births. Although WS is typically a sporadic disorder, familial cases have been reported.
WS is characterized by a variable combination of cardiovascular abnormalities, connective tissue abnormalities, distinct facial features, infantile hypercalcemia, mental retardation, and characteristic social interactions such as extreme friendliness and attention-deficit hyperactivity disorder.
Isolated congenital narrowing of the ascending aorta is common in WS patients and results in a separate syndrome called supravalvular aortic stenosis (SVAS).
WS is a contiguous gene deletion syndrome, caused by deletion of several genes on chromosome 7q. One gene that often is deleted in WS is the elastin gene, which causes SVAS and other cardiovascular disease in these patients. This association was described by Ewart et al (1993) who identified hemizygosity of the elastin gene in WS and SVAS.
The elastin gene, ELN, has been mapped to 7q11.23 (Williams syndrome chromosome region, and is reportedly hemizygous in up to 96% of patients with WS). The deletion of an elastin gene locus cannot be detected by conventional high-resolution chromosome analysis in the vast majority of cases due to the small size of this deletion. Nickerson et al used molecular methods to detect a deletion of the elastin gene in 91% (39/43) of WS patients.
In up to 1% of patients, WS is caused by a gene mutation within or near the elastin gene. These mutations would not be detected by this FISH test. FISH testing involves a DNA probe that detects only large deletions including this entire gene and the DNA probe, small deletions or mutations may give normal results by FISH.
Patients with a deletion outside of the elastin gene could display normal development of connective tissue, including the heart, but have other features of WS.
Reference Values
An interpretive report will be provided.
Cautions
Because this FISH test is not approved by the US Food and Drug Administration it is important to confirm Williams syndrome (WS) by other established methods, such as clinical history or physical evaluation.
Chromosomal microarray (CMAC / Chromosomal Microarray, Congenital, Blood or CMAP / Chromosomal Microarray, Prenatal) may be the more appropriate test to detect unbalanced translocations, deletions or duplications.
Interfering factors:
-Cell lysis caused by forcing the blood quickly through the needle
-Use of an improper anticoagulant or improperly mixing the blood with the anticoagulant
-Excessive transport time
-Inadequate amount of specimen may not permit adequate analysis
-Improper packaging may result in broken, leaky, and contaminated specimen during transport.
-Exposure of the specimen to temperature extremes (freezing or >30° C) may kill cells and interfere with attempts to culture cells.
-In prenatal specimens, a bloody specimen may interfere with attempts to culture cells and contamination by maternal cells may cause interpretive problems
Day(s) Performed
Samples processed Monday through Sunday. Results reported Monday through Friday, 8 a.m.-5 p.m. CST.
Report Available
10 daysPerforming Laboratory
Mayo Medical Laboratories in Rochester
Test Classification
This test was developed using an analyte specific reagent. Its performance characteristics were 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.CPT Code Information
88271x2, 88291 – DNA probe, each (first probe set), Interpretation and report
88271x2 – DNA probe, each; each additional probe set (if appropriate)
88271x1 – DNA probe, each; coverage for sets containing 3 probes (if appropriate)
88271x2 – DNA probe, each; coverage for sets containing 4 probes (if appropriate)
88271x3 – DNA probe, each; coverage for sets containing 5 probes (if appropriate)
88273 w/modifier 52-Chromosomal in situ hybridization, less than 10 cells (if appropriate)
88273-Chromosomal in situ hybridization, 10-30 cells (if appropriate)
88274 w/modifier 52 – Interphase in situ hybridization, <25 cells, each probe set (if appropriate)
88274 – Interphase in situ hybridization, 25 to 99 cells, each probe set (if appropriate)
88275 – Interphase in situ hybridization, 100 to 300 cells, each probe set (if appropriate)