Week 3a Flashcards
Genetics: What is direct diagnosis?
Type of genetic dx in which the mutation itself is examined
Genetics: what is indirect diagnosis?
Dx in which linked markers are used to infer whether the individual has inherited the chromosome segment containing the disease-causing mutation
PCR & Allele-Specific Oligonucleotide Probes (ASO) are used for what type of genetic testing
PCR & ASO are used in direct diagnosis of genetic disorders
What do ASO probes stand for?
Describe how it works
- Allele-Specific Oligonucleotide probes
- Have oligonucleotides that are complementary to the target allele sequence (Normal or Mutant). DNA from family, PCR to amplify DNA & spotted onto a Southern Hybridization filter. The filter is probed with a radioactive probe (the labeled oligonucleotide)
Hybridization of AZO probe conatining mutation = mutation
Hybridization of ASO probe for normal allele = normal.
Hybridization of both probes = heterozygote
ASO probes are best used to test for what specific genetic disorders?
Why?
- Sickle cell disease
- Hemochromatosis
- α1-antitrypsin deficiency
- Since a probe for normal, all mutant alleles must be generated, more practical when a limited number of mutations
Using _______ ___________ to test for sickle cell mutation, what is β S? What does β A mean?
- ASO Probes
- β S: Mutant allele
- β A: Normal allele
What are the advantages of direct diagnosis in genetic testing?
- Mutation itself is detected, family data is not necessary
- Direct diagnosis can be performed on any individual
- Error caused by recombination is not a factor, so dx accuracy is potentially higher than in indirect dx
If the mutation causing a disease in a family is not known, ______________ genetic analysis can often be used to infer whether a parent has transmitted the mutation to his or her offspring.
Indirect
_____________ __________________ ____________ is a good candidate for indirect genetic diagnosis.
Describe creatinine kinase levels in obligate carrier females than wild type females
- Duchenne muscular dystrophy
- Obligate carrier females with DMD normally have higher CK levels than wild type females.
Indirect genetic diagnosis: Describe linkage analysis
- Has to do with linked and unlinked genes
- During recombination, if two genes are segregated and recombined then the genes are unlinked
- If they travel together and do not experience recombination = Complete linkage
- Used to det. Whether a parent who carries a mutation has transmitted it to his or her offspring
What type of inheritance pattern does Marfan syndrome follow?
Autosomal dominant
Carrier diagnosis in recessive disease _________ genetic testing: _____________ ________________ is best.
Carrier diagnosis in recessive disease, direct genetic testing PCR + ASO is best
What genetic testing is best used for presymptomatic diagnosis for late-onset disease?
Give some examples:
- Indirect Linkage analysis
- Huntington disease, familial breast cancer, hemochromatosis, adenomatous polyposis
Asymptomatic diagnosis for diseases with reduced penetrance, what type of genetic testing is best used?
- Linkage, indirect
- PC + ASO, direct
Both can be used
What type of genetic testing is best for preimplantation testing?
PCR + sequencing
List the three invasive techniques involved in prenatal diagnosis
- Chordocentesis
- Amniocentesis
- Chorionic villus sampling
When is prenatal diagnosis performed?
11-14 wks gestation
What type of thickening is suspicious for Downs Syndrome?
Where might it be first detected?
- Nuchal thickening/translucency is an accumulation of fluid at the back of the neck
- Seen on U/S performed 11-14 wk gestation
List Blood Tests used in 1st &/or second trimester for serum screening of Down syndrome
- PAPP-A
- αFP
- uE3
- hCG β subunit
- Inhibin A
Describe in what tests would the serum level be down in serum screening for Down syndrome?
- PAPP-A
- αFP
- uE3
Describe in what tests would the serum level be high in screening for Down syndrome?
- hCG β subunit
- Inhibin A
What is cordocentesis?
When is it performed?
- Performed 18-24 weeks gestation after the umbilical cord has adequately developed
- Taking blood sample from one of the blood vessels in the fetus’s umbilical cord
What is amniocentesis?
When is it performed?
- Performed 16 weeks gestation
- Extract amniotic fluid to extract DNA
- 1/200 risk
What is chorionic villus sampling?
When is it performed?
- 10-12 weeks gestation
- Invasive technique that is removal of a small sample of chorionic villus material which are actively dividing fetal cells
What are the risks of chorionic villus sampling?
- Higher fetal mortality rate than with amniocentesis (1/100)
- Small possibility of diagnostic error b/c of placental mosaicism
