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FISH for Aneuploidy – For Doctors

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The Role of FISH in Prenatal and Postnatal Diagnosis

Fluorescence In Situ Hybridization (FISH) is a highly sensitive and rapid molecular cytogenetic test used to detect numerical chromosomal abnormalities. It is particularly useful in prenatal testing and neonatal screening.

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Indications for FISH Testing

FISH for aneuploidy (13, 18, 21, X, Y) is recommended for:

Conditions Detected by FISH

Condition Chromosome Clinical Features Sensitivity
Down syndrome Trisomy 21 Intellectual disability, characteristic facial features >99%
Edwards syndrome Trisomy 18 Severe congenital anomalies, poor prognosis 98%
Patau syndrome Trisomy 13 Severe CNS and cardiac defects, very low survival 95%
Turner syndrome 45, X Short stature, infertility, cardiac issues 98%
Klinefelter syndrome 47, XXY Hypogonadism, learning disabilities, infertility 97%

Methodology: How FISH Works

  • Sample Preparation: Cells from AF, CVS, blood are cultured or directly analyzed.
  • Hybridization: Fluorescent-labeled DNA probes specific to chromosomes 13, 18, 21, X, and Y bind to complementary sequences.
  • Microscopy Analysis: Under a fluorescence microscope, normal cells show two signals per chromosome, while aneuploidies display three (trisomy) or one (monosomy) signals.

Comparison

FISH vs. Other Prenatal Tests

Feature FISH QF-PCR Karyotyping Microarray
Detection Method Fluorescent probes STR markers G-banding High-resolution genome-wide scan
Results TAT 24–48 hours 24–48 hours 10–14 days ~7 days
Resolution Only detects aneuploidies (13, 18, 21, X, Y) Only aneuploidies Detects all large chromosomal abnormalities Detects submicroscopic deletions/duplications
Use Case Rapid detection of trisomies Rapid aneuploidy screening Comprehensive karyotype High-resolution for complex cases

Limitations of FISH for Aneuploidy

Cannot detect structural chromosomal abnormalities (translocations, inversions).

Limited to chromosomes 13, 18, 21, X, and Y.

False positives/negatives possible in cases of mosaicism.

Clinical Guidelines

Key Clinical Guidelines Supporting FISH

  • ACMG (2022): Supports FISH as a rapid screening tool for common aneuploidies.
  • ISPD (2023): Recommends FISH for urgent prenatal diagnosis but advises follow-up with karyotyping or microarray.

Why Choose Suraksha Genomics for FISH Testing?

  • Results within 24–48 hours for faster clinical decisions.
  • Expert interpretation by trained cytogeneticists.
  • Integration with full prenatal diagnostic services (QF-PCR, Karyotyping, Microarray).
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