Molecular cytogenetics

Question 1

FISH

Answer 1

Fluorescence in situ hybridization
Probes can target specific chromosomal regions:
		Centromeric
		telomeric
		locus-specific
		whole chromosome

Adv: can be used in all stages of cell cycle (interphase), can analyze cells (tumor cells removed)

Question 2

CGH

Answer 2

Comparative Genomic Hybridization

Evaluates the gains and losses in regions;aneuploidy

Adv: allows rapid screening of chromosomal imbalances, greater resolution, overcomes chromosome preparation barrier
Data gives a ratio of Control DNA: test DNA

Question 3

Locus Specific FISH probes

Answer 3

Helpful to detect microdelection syndromes ~1MB

Also use a control probe to identify specific chromosome of interest, in addition to specific locus

Question 4

Sub-telomeric FISH probes

Answer 4

Unique telomere region is the site of FISH probes

Contains the highest concentration of genes of any chromosome region

Ex: rearrangements not visible by karyotype G banding have been found in 4-9% of ppl with idiopathic MR

Question 5

Centromeric FISH probes

Answer 5

Information in non-cycling cells:
Uncultured cells (amniotic fluid)
fixed cells (tumors)
low mitotic index samples (chemo pts, post-bone marrow transplant)

Takes two days for results
Target viable trisomies: 13, 18, 21, sex chromosomes

Question 6

Whole chromosome paint

Answer 6

Used to detect translocations and can distinguish between balanced and unbalanced

Can also be used to identify from which chromosome a marker chromosome came from

10x more common in mentally subnormal
1/3-1/2 are inherited
if not inherited, and an autosomal ring –> 30% risk of abnormalities

Can also do mulit-color to label all chromosomes

Question 7

Chromosome analysis for cancer

Answer 7

1. Look for recurrent chromosome abnormalities which may have significance with respect to diagnosis, prognosis, and treatment
2. Identify copy number variations to provide personalized care; allows physicians to cound cell by cell and determine the percentage of cells affected

Question 8

FISH evaluation of leukemia

Answer 8

1. BRC/ABL gene fusion in chronic myelogenous leukemia (simple translocation or submicroscopic) on Philadelphia chromosome
2. Led to development of Imatinib (Gleevec) to specifically rarget the ABL gene (tyrosine kinase)

Question 9

FISH evaluation of gene amplification in tumors

Answer 9

1. HER2/NEU in breast cancer or MYCN amplification in neuroblastoma
2. Only 20-30% of patients are positive for gene amplification and must be treated differently
3. Herceptin treatment