FISH

Question 1

What types of FISH probes exist?

Answer 1

repetitive DNA probes

Whole/paint probes

unique DNA/sequence probes

Question 2

When would you use paint probes? what do they do?

When are they not useful?

Answer 2

useful for marker chromosomes, translocations, and aneuploidy in meta. cells

cover length of entire chromosome or chr arm

not useful in interphase cells

Question 3

What probes bind to the centromere? when are these useful? what chromosomes do they confuse?

Answer 3

alpha satellite probes

useful for detecting aneuploidy

13 and 21, 14 adn 22 are too similar

Question 4

What’s the difference between telomere and subtelomeric probes?

Answer 4

telomere: hybridizes to DNA tandem repeat TTAGGG at terminal ends

sub-: bind to unique DNA sequences immediately proximal to telomere repeats (specific to chromosomes)

Question 5

When are locus-specific probes useful?

Answer 5

deletions, duplications, and rearrangements

especially detecting translocations in interphase studies

Question 6

What can we test with FISH?

Answer 6

metaphase cells

interphase cells

direct preparations

paraffin embedded tissue sections

Question 7

FISH can be used to:

Answer 7

identify numerical abn and to characterize structural rearrangements

Question 8

what can produce false results during prenatal interphase FISH results?

Answer 8

polymorphisms

insertion of alpha-satellite sequence from one centromere into another

Question 9

What can go undetected during prenatal interphase FISH? why?

Answer 9

mosaicism

it is too low to be detected

MCC dilutes aneuploid cell ine

Question 10

What are the cutoffs to call mosaicism?

Answer 10

0-10%: normal

11-60%: inconclusive

> 60%: abn (mosaic)

Question 11

what are the limitations of prenatal interphase FISH? its purpose?

Answer 11

estimated 20-35% of visible abn will go undetected (mostly # and structural abn of untested regions) -> considered screening

used to detect common aneuploidy (13, 18, 21, X, and Y)

Question 12

what types of syndromes are associated with small, recurring interstitial deletions that are associated with a specific phenotype?

Answer 12

microdeletion

Question 13

What deletion is repsonsible for DiGeorge syndrome?

Answer 13

22q11.2

Question 14

Common indications of 22q11.2 deletion?

Answer 14

facial features, abn palate, CHD, learning problems, hypocalcemia, immune deficiency, and psychiatric disorders

Question 15

How many patients with DiGeorge syndrome have a cytogenetically visible deletion?

Answer 15

25%

Question 16

What does it mean if someone with 22q11.2 has an atypical deletion?

Answer 16

at least one breakpoint is not in the typical A-D region

Question 17

What percentage of 22q11.2 deletions are de novo?

Answer 17

90%

Question 18

What are a few of the limitations of FISH for 22q11.2 deletion syndrome?

Answer 18

only capable of detecting very large deletions that alter hybridization

some deletions are outside of the critical region (probe) and will go undetected

Question 19

What are complementary to microdeletion syndromes?

Answer 19

microduplications

Question 20

what is the common mechanism for complementary duplications and deletions?

Answer 20

nonallelic homologous recombination

Question 21

What is often true of complementary microduplication syndromes?

Answer 21

phenotypes are mild/uncharacterized

variable expression and penetrance

cytogenetically crytpic

Question 22

What is necessary to provide accurate counseling for apparent/known deletions?

Answer 22

parental karyotype or FISH

Question 23

What setting is FISH commonly used to monitor patietns?

Answer 23

oncology (hematological malignancies)