Description

Fluorescence In Situ Hybridization (FISH) is a powerful cytogenetic technique used to detect and localize the presence or absence of specific DNA sequences on chromosomes. The FISH – Myelodysplastic Syndrome (MDS) panel is designed to identify chromosomal abnormalities associated with MDS, a group of bone marrow disorders characterized by ineffective hematopoiesis and a risk of progression to acute myeloid leukemia (AML). The panel typically includes probes for specific regions on chromosomes 5, 7, 8, and 20.

FISH – MDS Panel Overview

1. Chromosome 5q (5q31):
   • Deletion of 5q (del(5q)): Common in MDS and is associated with a distinct clinical syndrome characterized by anemia, normal or elevated platelet counts, and a relatively good prognosis.
2. Chromosome 7q (7q22 or 7q31):
   • Deletion of 7q (del(7q)): Often associated with poor prognosis in MDS and AML. It is indicative of a more aggressive disease course and poorer response to treatment.
3. Chromosome 8q (8q24):
   • Trisomy 8 (+8): An additional copy of chromosome 8. It is one of the most frequent abnormalities in MDS and can be found in isolation or in combination with other cytogenetic abnormalities. Its prognostic significance varies depending on the presence of other abnormalities.
4. Chromosome 20q (20q12):
   • Deletion of 20q (del(20q)): Associated with a relatively favorable prognosis in MDS, especially when found in isolation without other adverse cytogenetic abnormalities.

Procedure

1. Sample Collection: Bone marrow or peripheral blood samples are collected from the patient.
2. Preparation: Cells are cultured, harvested, and prepared on slides.
3. Hybridization: Fluorescently labeled DNA probes specific to the regions of interest on chromosomes 5q, 7q, 8q, and 20q are applied to the prepared slides. The probes hybridize to their complementary DNA sequences on the patient’s chromosomes.
4. Detection: The slides are examined under a fluorescence microscope. The presence or absence of fluorescent signals indicates the presence or absence of the targeted chromosomal regions.

Interpretation

• Normal Result: Presence of normal fluorescent signals for chromosomes 5q, 7q, 8q, and 20q, indicating no detectable deletions or trisomies in these regions.
• Abnormal Result: Absence of signals (deletion) or additional signals (trisomy) indicating chromosomal abnormalities associated with MDS.

Clinical Significance

• Diagnosis: Helps confirm the diagnosis of MDS by identifying characteristic chromosomal abnormalities.
• Prognosis: Provides prognostic information based on the specific abnormalities detected. Certain deletions (e.g., del(5q)) are associated with better prognosis, while others (e.g., del(7q)) indicate a poorer prognosis.
• Treatment Planning: Guides therapeutic decisions, such as the use of targeted therapies like lenalidomide for patients with del(5q) MDS.

Follow-Up

• Monitoring: Regular follow-up and additional testing may be necessary to monitor disease progression or response to treatment.
• Additional Testing: In some cases, further genetic and molecular testing may be recommended to provide a comprehensive understanding of the patient’s disease.

The FISH – MDS panel is a valuable tool in the diagnosis and management of MDS, offering critical insights into the genetic abnormalities that drive the disease and influence its clinical behavior.