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HelpTest ID BP1F 15q Deletion, Type I and Type II Characterization, Prader-Willi/Angelman Syndromes, FISH
Useful For
Differentiating between type I and type II deletions in patients with a known deletion of 15q11.1-11.3, causative of Prader-Willi syndrome or Angelman
Evaluation of dic(15) marker chromosomes
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 |
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 application of 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
15q Del Characterization, FISHSpecimen Type
VariesThis test can only be performed if a known SNRPN or D15S10 deletion has been previously identified by FISH analysis or in patients with a dic(15) chromosome.
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: 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:
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 a 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
Amniotic Fluid: 5 mL/Autopsy, Skin Biopsy: 4 mm/Blood: 2 mL/Chorionic Villi: 5 mL/Fixed Cell Pellet: 1 pellet/Products of Conception: 1 cm(3)
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Varies | Refrigerated (preferred) | |
| Ambient | ||
Clinical Information
Prader-Willi (PWS) and Angelman (AS) syndromes are 2 distinct syndromes that can result from either a paternal or maternal deletion of 15q11-q13, respectively. Other mechanisms of inheritance include maternal uniparental disomy (UPD) in PWS, paternal UPD in AS, or abnormal methylation and gene expression.
Both type I and type II 15q11-q13 deletions have been described. Type 1 deletions are larger deletions, spanning breakpoint (BP)1 and distal BP3 breakpoints, while type II deletions are smaller (approximately 500kb), spanning BP2 and BP3. Depending on the deletion type, behavioral differences have been reported in both PWS and AS patients. Type I patients have more severe phenotypes including delayed development and autistic features. Distinguishing between type I and type II deletions is useful in counseling PWS or AS patients. Type I and II deletions may be detected by evaluating the RP11-289D12 region on chromosome 15 with specific DNA probes.
A +dic(15) marker chromosome (an extra or supernumerary dicentric chromosome 15) is often familial and is usually consistent with a normal phenotype, but depending on its size, the marker can be associated with PWS or AS. Larger dic(15) are usually new mutations and are associated with mental retardation and mild dysmorphic features.
See Prader-Willi and Angelman Syndromes: Laboratory Approach to Diagnosis in Special Instructions for additional information.
Reference Values
An interpretive report will be provided.
Cautions
Because this FISH test is not approved by the U.S. Food and Drug Administration, it is important to confirm type I and type II 15q11.2 deletions by other established methods, such as clinical history and physical evaluation.
This test is not designed to diagnose Prader-Willi/Angelman syndromes. 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. to 5 p.m. CST.
Report Available
7 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)
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)