FISH Flashcards
What types of FISH probes exist?
repetitive DNA probes
Whole/paint probes
unique DNA/sequence probes
When would you use paint probes? what do they do?
When are they not useful?
useful for marker chromosomes, translocations, and aneuploidy in meta. cells
cover length of entire chromosome or chr arm
not useful in interphase cells
What probes bind to the centromere? when are these useful? what chromosomes do they confuse?
alpha satellite probes
useful for detecting aneuploidy
13 and 21, 14 adn 22 are too similar
What’s the difference between telomere and subtelomeric probes?
telomere: hybridizes to DNA tandem repeat TTAGGG at terminal ends
sub-: bind to unique DNA sequences immediately proximal to telomere repeats (specific to chromosomes)
When are locus-specific probes useful?
deletions, duplications, and rearrangements
especially detecting translocations in interphase studies
What can we test with FISH?
metaphase cells
interphase cells
direct preparations
paraffin embedded tissue sections
FISH can be used to:
identify numerical abn and to characterize structural rearrangements
what can produce false results during prenatal interphase FISH results?
polymorphisms
insertion of alpha-satellite sequence from one centromere into another
What can go undetected during prenatal interphase FISH? why?
mosaicism
it is too low to be detected
MCC dilutes aneuploid cell ine
What are the cutoffs to call mosaicism?
0-10%: normal
11-60%: inconclusive
> 60%: abn (mosaic)
what are the limitations of prenatal interphase FISH? its purpose?
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)
what types of syndromes are associated with small, recurring interstitial deletions that are associated with a specific phenotype?
microdeletion
What deletion is repsonsible for DiGeorge syndrome?
22q11.2
Common indications of 22q11.2 deletion?
facial features, abn palate, CHD, learning problems, hypocalcemia, immune deficiency, and psychiatric disorders
How many patients with DiGeorge syndrome have a cytogenetically visible deletion?
25%
What does it mean if someone with 22q11.2 has an atypical deletion?
at least one breakpoint is not in the typical A-D region
What percentage of 22q11.2 deletions are de novo?
90%
What are a few of the limitations of FISH for 22q11.2 deletion syndrome?
only capable of detecting very large deletions that alter hybridization
some deletions are outside of the critical region (probe) and will go undetected
What are complementary to microdeletion syndromes?
microduplications
what is the common mechanism for complementary duplications and deletions?
nonallelic homologous recombination
What is often true of complementary microduplication syndromes?
phenotypes are mild/uncharacterized
variable expression and penetrance
cytogenetically crytpic
What is necessary to provide accurate counseling for apparent/known deletions?
parental karyotype or FISH
What setting is FISH commonly used to monitor patietns?
oncology (hematological malignancies)
