Chromosome Analysis: Hematological Disorders

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1) What is cytogenetics?

Cytogenetics is the study of the structure and function of chromosomes in relation to their phenotypic expression. It helps to characterize an individual’s genetic material. Chromosomal abnormalities are responsible for a wide variety of diseases and disorders which may be either cancers or defects by birth like Down or Turners syndrome.

2) What are the general indications of doing cytogenetic testing?

Usually, this testing is done under 2 scenarios:
i. Constitutional karyotyping on routine body cells to study genetic make-up of a person.
ii. Neoplastic cytogenetic testing on cancer cells to see their exact genetic composition, which helps in diagnosis and targeted therapies. This is of greater significance because chromosomal abnormalities play a central role in the pathogenesis of various malignancies. 

3) What are the commonly seen blood cancers?

Leukemias are cancer of blood-forming cells. ALL, CLL, AML, CML, and Multiple myeloma are the commonly occurring blood cancers. ALL is usually seen in paediatric ages, CLL and multiple myeloma in very elderly age population, AML occurs in young adults and CML is seen in 4th-5th decade of life. However there, no hard and fast age cut-offs, and all blood cancers can arise at different ages. Other groups of hematologic malignancies are myelodysplastic syndrome, myeloproliferative disorders, and lymphomas which are B-cell type and T-cell type.

4) In which hematological malignancies, this testing is less useful?

Conventional karyotyping studies are not very successful in B-cell disorders because B-lymphocytes do not grow well in cell culture which is the initial step in performing this test.
 
5) What is the role of bone marrow in our body?

Bone marrow is a soft part in the centre of the majority of bones where precursor stem cells of our blood cells reside from an individual’s birth. Its major role is production of hematopoietic cells which get distributed in the peripheral blood; thus it helps in formation of blood cells and its release into the bloodstream. 

6) What are hematopoietic or blood cells?

Blood cells are constituents of blood which includes red blood cells, white blood cells and platelets. Their precursors are present in bone marrow in immature form and from stem cells, these blood constituents get matured for functioning.

7) Can I directly ask for bone marrow cytogenetic testing if I have chronic symptoms? 

No. It is always the treating physician’s call. After correlating with other lab parameters, symptoms and clinical findings, the decision of doing cytogenetic testing is taken based upon suspicion of any chromosomal abnormality. 

8) Do I need to do any other test along with this?

There are few submicroscopic chromosomal abnormalities which cannot be seen on routine karyotyping analysis. In such cases advanced genetic and molecular testing like FISH - Fluorescence in situ hybridization and NGS - next-generation sequencing needs to be done to find out chromosomal defects in details. Also for plasma cell disorders, FISH testing is a much more useful tool for diagnosis and prognosis as compared to conventional karyotyping.


9) Below are the commonly found chromosomal abnormalities in various blood cancers:

 

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