Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test
About Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test
| Field | Value |
|---|---|
| Also Known As | PWS/AS FISH Test, FISH for 15q11-q13 Microdeletion Test, Angelman/Prader-Willi FISH Test, SNRPN FISH Test |
| Sample Type | Peripheral blood (sodium heparin tube) |
| Fasting Required | No fasting required |
| Report Time | 6 days |
| Recommended For | All ages; primarily infants and children with suspected developmental delays, poor muscle tone, or clinical features of Prader-Willi or Angelman syndrome |
| Price | Starting at ₹4,800 |
What is a Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test?
The Prader-Willi/Angelman Syndrome (FISH 15q11-13) test is a specialised genetic test that checks for missing genetic material in a specific region of chromosome 15. This region, known as 15q11-13, is linked to two distinct genetic conditions: Prader-Willi syndrome and Angelman syndrome.
The test uses a technique called fluorescence in situ hybridisation, commonly abbreviated as FISH, which uses fluorescent probes to identify chromosomal changes. A peripheral blood sample collected in a sodium heparin tube is used for analysis. This test is also known as the PWS/AS FISH test and the Angelman/Prader-Willi FISH test.
What Does a Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test Measure?
The FISH 15q11-13 test analyses specific genetic material on chromosome 15 to detect a microdeletion (a small piece of missing DNA) in the critical region associated with both syndromes. The table below outlines what the test looks for.
| Component | What It Detects |
|---|---|
| 15q11-13 chromosomal region | Presence or absence of genetic material in the region linked to PWS and AS |
| SNRPN gene locus | Integrity of the imprinting centre on chromosome 15, covered by the FISH probe |
| Control probe (chromosome 15 identifier) | Confirms chromosome 15 is present for comparison with the test probe signal |
A normal result shows two fluorescent signals, one on each copy of chromosome 15. A missing signal indicates a deletion in that region.
Why is a Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test Done?
A doctor may request the Prader-Willi/Angelman Syndrome (FISH 15q11-13) test when a child or infant shows signs that suggest either of these two genetic conditions. The clinical features of each syndrome are different, and the test helps confirm whether a chromosomal deletion is the underlying cause.
Common Symptoms That May Require This Test
The following signs may prompt a doctor to order this test, listed by the syndrome they are associated with.
Suspected Prader-Willi syndrome:
- Poor muscle tone (hypotonia) in a newborn
- Weak sucking and feeding difficulties in infancy
- Delayed physical and mental development
- Genital underdevelopment or short stature
- Excessive eating and weight gain in childhood
Suspected Angelman syndrome:
- Severe developmental delay or intellectual disability
- Absent or very limited speech
- Unsteady walking or trembling of the limbs
- Frequent laughing, smiling, and excitable behaviour
- Seizures or unusually small head size (microcephaly)
Conditions This Test Can Help Detect
The FISH 15q11-13 test is used to identify the following genetic conditions.
- Prader-Willi syndrome, which results from the absence of genetic material on the paternal copy of chromosome 15 in the 15q11-13 region
- Angelman syndrome, which results from the absence of genetic material on the maternal copy of the same region
- Chromosomal microdeletions of 3 to 4 Mb in the 15q11-13 region
How to Prepare and What to Expect
The Prader-Willi/Angelman Syndrome (FISH 15q11-13) test procedure is straightforward and requires no special preparation beforehand.
Do You Need to Fast?
No fasting is required for this test. You or your child may eat and drink normally before the sample is collected.
Practical Tips Before Your Test
The following points will help ensure the sample is collected and processed correctly:
- Bring a detailed clinical history, including symptoms, previous test results, and family history
- Inform the healthcare professional of any current medications
- Ensure the blood is collected specifically in a sodium heparin (green-top) tube, not any other tube type
- The sample must be stored and transported at ambient room temperature (20°C to 25°C) to keep the cells viable for laboratory culture
Step-by-Step Procedure
Here is what to expect during the Prader-Willi/Angelman Syndrome (FISH 15q11-13) test procedure.
- A trained phlebotomist cleans the skin over a vein, usually in the arm or, for infants, from an appropriate site.
- A small peripheral blood sample (3 ml) is drawn and collected into a sodium heparin tube.
- The tube is gently inverted to mix the blood with the anticoagulant.
- The sample is maintained at ambient room temperature (20°C to 25°C) and dispatched to the laboratory promptly. Do not freeze or refrigerate.
- In the laboratory, cells from the blood are cultured for 48 to 72 hours until enough dividing cells are available for analysis.
- Fluorescent probes targeting the 15q11-13 region are applied to the cell preparation. A pathologist then examines the signal pattern under a fluorescence microscope to determine whether a deletion is present.
Factors That Can Affect Accuracy
The following factors may affect the quality or reliability of the result:
- Using the wrong tube type (lithium heparin or other anticoagulants render the sample unacceptable)
- Clotted or frozen specimens cannot be processed
- Delays in transporting the sample to the laboratory
- Poor cell culture growth affecting the number of cells available for analysis
- Laboratory experience in reading FISH signal patterns
Understanding Your Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test Results
Results of the FISH 15q11-13 test reflect whether a microdeletion is present in the chromosome 15 region. A qualified geneticist or doctor will interpret these findings alongside clinical history and, if needed, additional tests.
| Parameter | Normal Result | Abnormal Result |
|---|---|---|
| 15q11-13 region signals | Two signals present (one on each chromosome 15) | One signal present, indicating a deletion on one chromosome |
| SNRPN locus signals | Two signals present | One signal present, indicating a deletion at the locus |
A normal pattern shows two red and two green signals (2R2G). An abnormal pattern with a microdeletion shows one red and two green signals (1R2G). A positive result is consistent with either Prader-Willi syndrome or Angelman syndrome. Because a standard FISH test cannot differentiate between a maternal or paternal deletion, clinical symptoms or a follow-up DNA methylation test are used to confirm the exact diagnosis
The FISH test detects approximately 70% of Prader-Willi syndrome cases and around 68% of Angelman syndrome cases. It does not detect other causes of these conditions, such as uniparental disomy (where both copies of chromosome 15 are inherited from one parent) or imprinting defects. A normal FISH result does not rule out these syndromes if clinical suspicion remains high.
Disclaimer: These results show chromosome structures, not standard fluid ranges. Your doctor will interpret findings based on clinical symptoms and history. Always consult a qualified specialist for diagnostic confirmation.
Long-Term Management & Support
This is a genetic diagnostic test, not a test of a physiological value that changes with diet or lifestyle. The following guidance is therefore framed differently.
- Seek genetic counselling before and after testing to understand what the results mean for your child and your family
- Use the test result as a starting point for planning appropriate therapies, developmental support, and specialist referrals
- Discuss family planning implications with a clinical geneticist, particularly if planning future pregnancies
Lupin Diagnostics Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test Price and Home Collection
The Prader-Willi/Angelman Syndrome (FISH 15q11-13) test is available at Lupin Diagnostics starting at ₹4,800, with home sample collection available across cities in India.
| City | Approximate Price (₹) |
|---|---|
| BHOPAL | 4800 |
| CHENNAI | 4800 |
| HYDERABAD | 4800 |
| KOLKATA | 4800 |
| NAVI MUMBAI | 4800 |
| PUNE | 4800 |
Disclaimer: Prices are indicative and may vary by location. Please confirm the current price at the time of booking.
How to Book
Follow these steps to book your Prader-Willi/Angelman Syndrome (FISH 15q11-13) test online.
- Select the test on the Lupin Diagnostics website
- Choose your city and preferred time slot
- Opt for home sample collection by a certified phlebotomist, or visit your nearest Lupin Diagnostics centre
- Receive your report via email or WhatsApp within 6 days
Home Collection
Lupin Diagnostics offers Prader-Willi/Angelman Syndrome (FISH 15q11-13) test home collection across multiple cities in India. All samples are processed in NABL-accredited laboratories by experienced professionals. Digital reports are made available promptly, allowing families and doctors to review results without delay.
Frequently Asked Questions
Both conditions are caused by the loss of genetic material in the 15q11-13 region of chromosome 15, but the parent from whom the deletion is inherited determines which condition results. When the paternal copy of this region is absent, Prader-Willi syndrome occurs; when the maternal copy is absent, Angelman syndrome results. Prader-Willi syndrome is associated with poor muscle tone in infancy and excessive eating later in childhood, while Angelman syndrome is characterised by severe intellectual disability, limited speech, and seizures.
The test detects deletions in approximately 70% of Prader-Willi syndrome cases and around 68% of Angelman syndrome cases. This means a normal result does not completely rule out either condition. If clinical signs remain, a doctor may recommend additional testing such as methylation analysis, which detects a broader range of genetic causes.
Yes. When there is a family history of either condition, the FISH test can be performed on fetal samples obtained through amniocentesis or chorionic villus sampling during pregnancy. This form of testing is typically recommended for families who have already had a child diagnosed with Prader-Willi or Angelman syndrome.
A normal FISH 15q11-13 test result does not exclude a diagnosis of Prader-Willi or Angelman syndrome. Around 25% of Prader-Willi syndrome cases are caused by maternal uniparental disomy, which the FISH test cannot detect. A doctor may then order methylation analysis or DNA polymorphism studies to investigate other possible causes.
No special preparation is needed. Fasting is not required. The key requirement is to bring a detailed clinical history, including symptoms and any previous test results, as this information is needed for accurate interpretation of the FISH result.
At Lupin Diagnostics, the report is typically delivered within 6 days of sample collection. This allows time for cell culture, FISH analysis, and expert review of the results by a trained pathologist.
A positive result should be discussed with a clinical geneticist or a specialist doctor experienced in rare genetic conditions. Early diagnosis helps families access appropriate therapies, educational support, and developmental interventions. Genetic counselling is strongly recommended to understand the implications for both the child and future family planning.
Prader-Willi/Angelman Syndrome (FISH 15q11-13) Test
