Molecular Cytogenetics

Question 1

Acute Pro-Myeloid leukemia

Answer 1

t(15;17)(q24;q21)

Treated with retinoic acid and arsenic trioxide that inhibit cell division and active cell differentiation.

Question 2

Chronic Myeloid Leukemia (CML)

Answer 2

t(9;22)(q34;q11.2)

Treatment: with a tyrosine kinase inhibitor called Imatinib Mesylate or Gleevec that inhibits cell proliferation.

Question 3

Describe the common cytogenetic findings in childhood B-cell leukemia and how the cytogenetic findings influence patient prognosis.

Answer 3

Bone marrow cells in patients with acute lymphoblastic leukemia (ALL) have dividing cells that are normal with 46,XXorXY karyotype and blasts that are part of the disease, an acquired abnormality.

These cells can have many cytogenetic changes including hyperdiploidy and hypodiploidy.

Cells with hyperdiploidy (i.e. more than 50 chromosomes typically with trisomy 4, 10, and 17 in particular) lead to a good prognosis, while cells with hypodiploidy (i.e. less than 45 chromosomes) lead to a poor prognosis.

Question 4

Delineate types of fluorescence in situ hybridization (FISH) probes and how they complement standard cytogenetic analysis, particularly in hematologic.

Answer 4

Centromere (cen): These FISH probes bind to regions near the centromeres of chromosomes. Usually used to quantify the number (enumeration) of chromosomes in a cell, e.g. hyperdiploid or hypodiploid blasts in ALL (Acute lymphoblastic leukemia).

Question 5

Fish Proble:

Fusion (F or DF)- dual fusion

Answer 5

These FISH probes are used to identify translocations, e.g.

t(15;17) FOR APML

t(9;22) for CML

Used in BCR; ABL or PML:RAR-a or in cancer detection.

Question 6

Locus specific identifier (LSI)

Answer 6

These FISH probes are used to identify deletions/duplications

specific to particular disease.

For example, deletion of 22q11.2 in DiGeorge syndrome, and to find p53 mutations in cancer.

Question 7

Fish probe:

Break Apart (BAP)

Answer 7

Used for finding translocations rearrangements

For example in MLL (cancer)

Question 8

Explain the roles of chromosomal microarray (CMA) analysis:

Deletions shown as RED

Duplications shown as Green

Cannot detect balanced translocations such as rearrangements.

Answer 8

Chromosomal microarray (CMA) analysis uses fluorescent technology to survey every chromosome for deletions or duplications. Patient DNA is labeled with green fluorescent dye and a reference DNA is labeled with red fluorescent dye. The two labeled DNAs are then mixed and hybridized to the array. After post-hybridization washes, the arrays are viewed in a fluorescent scanner and a statistical test is performed to measure the color intensities. If there is an equal level of patient and reference DNA, the signal will appear yellow in the fluorescent scanner. If a segment of patient DNA is deleted, the signal will appear red. If a segment of patient DNA is duplicated, the signal appears green. Thus, the whole genome can be analyzed simultaneously. CMA analysis can detect deletions or duplications that cannot be seen by standard cytogenetic analysis, but it cannot ****detect balanced rearrangements such as translocations. CMA analysis is also limited for detecting mosaicism.

Question 9

APML can be detected by fish proble (DF) by binding to_________. APML has characteristic Auer rods.

CML can be detected by fish probe binding to _________.

Answer 9

PML: RAR-a

ABL: BRC

Question 10

How is CML treated?

Answer 10

By Imatinib (gleevec), by acting as a molecular antagonist that binds to the ATP binding site in ABL tyrosine kinase and ABL/BRC tysone kinase. Thus, it inhibits cell proliferation.