13q14, CEP 18, 21q22.13, CEP X, CEP Y
Trisomy 13, trisomy 18, trisomy 21, aneuploidy X or Y
Fluorescence in situ Hybridization (FISH)
*Performed by affiliate laboratory
FFPE tissue is acceptable for FISH analysis. Preferred fixative is 10% neutral buffered formalin. Tissues preserved in B5 fixative or decalcified are usually not suitable for FISH. Tumor sections cut 3-5 µm thick and mounted on positively charged organosilane coated (silanized) slides work well. Request several unstained sections (two for each probe) and one H&E stained slide
4°C to 25°C during transit, but specimens may be transported on refrigerated gel packs. Do not allow the gel pack to come in contact with the specimen. Do not freeze. Extreme temperatures should be avoided.
Inadequate fixation; Improper labeling
Normal analysis: XX or XY with no evidence of aneuploidy for chromosomes 13, 18 or 21
Conventional cytogenetic evaluation is required for prenatal and newborn cases when aneuploidy FISH is requested (typically chromosomes X,Y,13,18 and 21). If the FISH result is abnormal, chromosome analysis can determine whether the abnormality is due to aneuploidy or a complex structural abnormality and will enable a more accurate recurrence risk for the family. If the FISH result is normal, a chromosome analysis allows identification of more complex abnormalities and the less common numeric abnormalities of other chromosomes.
Trisomy 13, trisomy 18 and trisomy 21, and numerical errors of the sex chromosomes (X and Y) constitute the most common chromosome abnormalities observed at prenatal diagnosis. DNA probes specific for chromosomes 13, 18, 21, X and Y permit enumeration of these chromosomes in uncultured (interphase) cells.
A major benefit of using uncultured cells is that test results are typically available within 24 hours of sample receipt, significantly reducing maternal anxiety. Another advantage is the ability to implement pregnancy management options in a timely manner when abnormal FISH results are associated with atypical ultrasound findings or other unfavorable clinical information. The ability to perform chromosome enumeration on uncultured cells is also a valuable alternative in the event of growth failure or suboptimal growth of cultured cells.
Although detection of aneuploidy of chromosomes 13, 18, 21, X and Y is highly accurate, this test does not detect other numerical abnormalities or structural chromosome aberrations. Prenatal FISH studies should be accompanied by routine cytogenetic analysis to confirm a normal fetal karyotype.
In the absence of fresh tissue, testing on FFPE tissue may be used as part of the evaluation for a partial molar pregnancy.