FISH - Prader-Willi Syndrome / SNRPN Test
Short Name: FISH - PWS/SNRPN
Also known as: PWS FISH Test, SNRPN Deletion Test, Prader-Willi FISH Analysis, Chromosome 15q11-q13 FISH Test, PWS/SNRPN Fluorescence In Situ Hybridization Test
FISH - Prader-Willi Syndrome / SNRPN Test test available at DNA Labs India for ₹9,000. Uses FISH (Fluorescence In Situ Hybridization) on Whole Blood samples. Results in Sample acceptance: Daily by 4:00 PM. Report delivery: Within 4 working days from sample receipt. Reports are delivered through the online portal, email, and WhatsApp.. Free home collection in 300+ cities across India.
🩺 Medically Reviewed By
Dr SULOCHANA HEMCHANDRA HOLLA
Consultant Medical Geneticist · Reg: 8532
Last reviewed: September 7, 2026
Overview
The primary purpose of the FISH - Prader-Willi Syndrome / SNRPN Test is to detect deletions in the SNRPN gene region on chromosome 15q11-q13, which is the most common genetic cause of Prader-Willi Syndrome. This test helps confirm a clinical diagnosis of PWS, guides treatment and management decisions, provides genetic counselling information for families, and distinguishes PWS from Angelman Syndrome and other conditions with overlapping clinical features.
- Test Code
- 610
- CPT Code
- 88271
- ICD Code
- Q87.1
- Price
- ₹9,000
- Sample Type
- Whole Blood
- Result Time
- Sample acceptance: Daily by 4:00 PM. Report delivery: Within 4 working days from sample receipt. Reports are delivered through the online portal, email, and WhatsApp.
- Fasting Required
- No
- Method
- FISH (Fluorescence In Situ Hybridization)
Sample Collection
Duly filled Chromosome & FISH analysis Requisition Form (Form 17) is mandatory. No fasting is required. Inform the healthcare provider about any medications or recent blood transfusions.
Method: Venipuncture
Laboratory Analysis
A blood sample of 5 mL (minimum 3 mL) will be collected from a vein in the arm using standard venipuncture technique into a Green Top (Sodium Heparin) tube.
Report Delivery
Apply gentle pressure to the puncture site with a cotton ball or gauze for a few minutes. The sample will be shipped at 18-22°C. The sample must NOT be frozen. Reports will be available within 4 working days.
Timeline: Sample acceptance: Daily by 4:00 PM. Report delivery: Within 4 working days from sample receipt. Reports are delivered through the online portal, email, and WhatsApp.
Patient Instructions
About This Test
Who Should Get This Test
The primary purpose of the FISH - Prader-Willi Syndrome / SNRPN Test is to detect deletions in the SNRPN gene region on chromosome 15q11-q13, which is the most common genetic cause of Prader-Willi Syndrome. This test helps confirm a clinical diagnosis of PWS, guides treatment and management decisions, provides genetic counselling information for families, and distinguishes PWS from Angelman Syndrome and other conditions with overlapping clinical features.
How to Prepare
- Collect 5 mL (minimum 3 mL) of whole blood by venipuncture
- Use 1 Green Top (Sodium Heparin) tube only
- Ship the sample at 18-22°C - DO NOT FREEZE
- Duly filled Chromosome & FISH analysis Requisition Form (Form 17) is mandatory
- Sample must reach the laboratory by 4:00 PM daily for same-day processing
- Label the tube correctly with patient name, date of birth, and sample date
Doctor's Notes
Reviewed by Dr SULOCHANA HEMCHANDRA HOLLA — MBBS, MD (Medical Genetics) · Reg. No. 8532
"As an obstetrician-gynecologist, I encounter cases where prenatal or neonatal findings such as decreased fetal movement, polyhydramnios, or severe neonatal hypotonia with feeding difficulties may raise suspicion for Prader-Willi Syndrome. Confirmatory genetic testing using FISH for the SNRPN gene is essential for establishing a definitive diagnosis. Early identification allows families to access appropriate nutritional management, growth hormone therapy, and developmental support programs. I recommend this test for any infant presenting with unexplained hypotonia and poor feeding in the neonatal period, as well as for families with a history of PWS seeking prenatal or postnatal confirmation."
Last medically reviewed: September 7, 2026
Test Parameters & Specifications
Sample Stability
- Sample collected in a tube other than Green Top (Sodium Heparin)
- Frozen sample received at the laboratory
- Missing or incomplete Chromosome & FISH analysis Requisition Form (Form 17)
- Sample volume less than 3 mL
- Haemolysed or contaminated sample
- Sample received after 48 hours of collection at room temperature
- Unlabelled or mislabelled sample
Understanding Your Results
Absence of one FISH signal for the SNRPN gene locus on chromosome 15q11-q13 indicates a deletion in the paternal copy of the imprinted region. This finding is consistent with a diagnosis of Prader-Willi Syndrome, accounting for approximately 70% of all PWS cases. Clinical correlation and genetic counselling are recommended.
Result type: Positive - Deletion Detected
Two normal FISH signals for the SNRPN gene locus indicate no deletion in the 15q11-q13 region. However, this result does not completely rule out Prader-Willi Syndrome, as approximately 25-30% of PWS cases are caused by maternal uniparental disomy (UPD) or imprinting centre defects, which are not detectable by FISH. Additional testing such as methylation-specific PCR or chromosomal microarray analysis may be recommended.
Result type: Negative - No Deletion Detected
If results are unclear due to technical issues, insufficient cell count, or ambiguous signal patterns, repeat testing or alternative molecular methods such as methylation analysis or chromosomal microarray may be required.
Result type: Equivocal / Inconclusive
Consult your healthcare provider or a clinical geneticist if the test result is positive for SNRPN deletion (confirming Prader-Willi Syndrome), if the result is negative but clinical suspicion for PWS remains high, or if you need guidance regarding genetic counselling, family planning, or management options for Prader-Willi Syndrome. Early intervention with a multidisciplinary team including endocrinologists, nutritionists, and developmental specialists is recommended for confirmed cases.
Limitations
- ⚠FISH detects large deletions (typically 5-7 Mb) in the 15q11-q13 region but may not identify PWS caused by uniparental disomy (UPD), imprinting centre defects, or point mutations in the SNRPN gene
- ⚠This test specifically targets the SNRPN gene region; a negative result does not completely rule out Prader-Willi Syndrome
- ⚠Methylation studies or chromosomal microarray analysis may be required as complementary tests for comprehensive diagnosis
- ⚠Mosaicism may not always be detected by standard FISH analysis
- ⚠This test does not provide information about the size of the deletion or breakpoints at the molecular level
Risks & Considerations
- ●Mild pain or discomfort at the venipuncture site
- ●Minor bruising or haematoma at the puncture site
- ●Rare risk of infection at the collection site
- ●Fainting or dizziness in individuals sensitive to blood draws
Interfering Factors
- ●Poor sample quality or insufficient cell viability
- ●Inadequate number of metaphase cells or interphase nuclei for analysis
- ●Sample contamination or haemolysis
- ●Exposure of the sample to freezing temperatures during transport
- ●Use of incorrect anticoagulant (must be Sodium Heparin / Green Top tube)
Compare With Similar Tests
| Test | FISH - Prader-Willi Syndrome / SNRPN Test | Methylation-Specific PCR | Chromosomal Microarray Analysis (CMA) | Standard Karyotype Analysis |
|---|---|---|---|---|
| Comparison | FISH - Prader-Willi Syndrome / SNRPN Test |
Frequently Asked Questions
What is the FISH - Prader-Willi Syndrome / SNRPN Test?
What is Prader-Willi Syndrome (PWS)?
What are the symptoms of Prader-Willi Syndrome?
What sample is required for the FISH SNRPN test?
What does a positive (deletion detected) FISH SNRPN test result mean?
What does a negative (no deletion detected) FISH SNRPN test result mean?
At what age can the FISH SNRPN test be performed?
Is the FISH test the only way to diagnose Prader-Willi Syndrome?
What is the cost of the FISH - Prader-Willi Syndrome / SNRPN Test at DNA Labs India?
Is home sample collection available for this test?
How long does it take to get the FISH SNRPN test results?
Is the FISH SNRPN test covered by health insurance in India?
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