Question
| A. |
Fluorescent in situ hybridisation |
| B. |
Karyotyping |
| C. |
Immunohistochemistry |
| D. |
Sanger’s technique |
|
Correct Answer � A Explanation |
 |
Fluorescent in situ hybridization (FISH) is a molecular cytogenetic technique used to visualize and identify specific DNA sequences within cells and tissues. This technique involves the use of fluorescently labeled probes that are complementary to target DNA sequences.
When applied to a sample, these probes hybridize, or bind, to the complementary DNA sequence, allowing it to be visualized under a fluorescence microscope. This binding of two complementary nucleic acid strands to form a stable double-stranded molecule is the principle underlying hybridization.
FISH is particularly useful for detecting genetic abnormalities, such as chromosomal rearrangements, deletions, duplications, and translocations. In the context of Ewing sarcoma, FISH is commonly used to detect rearrangements in the EWSR1 gene.
Ewing sarcoma is characterized by a specific translocation between chromosomes 11 and 22, written as t(11;22)(q24;q12), which results in the fusion of the EWSR1 gene with the FLI1 gene. This fusion is a hallmark of Ewing sarcoma and can be visualized using FISH, thus confirming the diagnosis.
The image provided demonstrates the FISH technique, with fluorescent probes highlighting genetic sequences, allowing for the identification of EWSR1 gene rearrangements in Ewing sarcoma.
Other Options:
Karyotyping
- Description: Karyotyping is a technique used to examine the entire chromosome set of an individual. It can detect large chromosomal abnormalities such as aneuploidies, translocations, deletions, and duplications.
- Limitations: While it provides a broad view of chromosomal structure, it lacks the sensitivity to detect small gene rearrangements or specific translocations like the EWSR1-FLI1 fusion seen in Ewing sarcoma.
Immunohistochemistry (IHC)
- Description: Immunohistochemistry is a method that uses antibodies to detect specific proteins in cells or tissue sections. It is widely used to identify cell types, markers of differentiation, and the presence of specific antigens in tumors.
- Limitations: IHC does not detect DNA or chromosomal abnormalities directly. It is useful for identifying protein expression but cannot confirm genetic rearrangements such as the EWSR1-FLI1 translocation.
Sanger Sequencing
- Description: Sanger sequencing is a DNA sequencing technique used to determine the exact nucleotide sequence of a specific DNA segment. It is highly accurate for detecting point mutations or small indels (insertions or deletions).
- Limitations: Sanger sequencing is not suitable for identifying large structural rearrangements like translocations. Therefore, it is not typically used to detect the EWSR1-FLI1 fusion in Ewing sarcoma.
