Fluorescence in situ hybridisation (FISH) is used to detect chromosomal abnormalities. A patient with suspected Philadelphia chromosome t(9;22) translocation is tested by dual-colour FISH. A positive result shows fusion of BCR (chromosome 22, red) and ABL1 (chromosome 9, green) probes. What would be observed in a positive FISH result?
- A Complete absence of both red and green signals due to chromosomal deletion
- B Amplification of green signals only, indicating ABL1 gene amplification
- C Yellow (co-localised) fusion signals in addition to isolated red and green signals, representing the derivative Philadelphia chromosome carrying BCR-ABL1 ✓
- D Three separate red signals and three separate green signals indicating trisomy
Explanation
In dual-fusion FISH for BCR-ABL1, a normal cell shows two separate red (BCR, chr 22) and two separate green (ABL1, chr 9) signals. In a positive (CML) cell with t(9;22), one BCR (red) and one ABL1 (green) probe are brought into adjacency on the Philadelphia chromosome, producing a yellow (co-localised) fusion signal. The cell also retains one normal chr 22 (red) and one normal chr 9 (green), so the typical CML pattern is: 1 yellow fusion + 1 red + 1 green. This is the basis of dual-fusion FISH used in CML diagnosis and MRD monitoring. RT-PCR for BCR-ABL1 mRNA is more sensitive for quantitative MRD.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.