Genetics Flashcards
At what gestation can you perform chorionic villus sampling to sample baby DNA?
Where is this sample actually taken from?
What is the miscarriage rate?
What is the viability of the tissue?
11.5 weeks onwards
Placenta
1-2%
Good
When doing a chorionic villus sample, there is a risk of confined placental mosaicism - what does this mean?
Lots of cells are dividing rapidly in the placenta, so a lot of genetic abnormalities form which do not cause any harm to the foetus
Pulling one of these cells can result in false positives
At what gestation can you perform amniocentesis to sample baby DNA?
Where does this sample actually come from?
What is the miscarriage rate?
What is the viability of the tissue?
15 weeks onwards
Skin/urine cells
0.5-1%
Poor
At what gestation can you perform foetal blood sampling to assess baby DNA?
What is the miscarriage rate?
What is the viability of the tissue?
Is this commonly used?
18 weeks onwards
1-2%
Good
No
At what gestation can you perform non-invasive prenatal testing?
Where does this sample come from?
What is the miscarriage rate?
8 weeks onwards
Maternal blood
0%
Once you have extracted DNA from a baby, what is the most effective way of analysing that DNA (whole genome wide)?
Once you have extracted DNA from a baby, what is the most effective way of analysing that DNA (for targeted testing)?
Array CGH
Fluorescent PCR
At 20 weeks, a mother gets a further US scan to assess for features of Down’s - if the probability of the child having Down’s is greater than 1/150 then the mother should be offered what test?
Amniocentesis
What can non-invasive prenatal testing currently be used for?
Sex selection - only if at risk of a disease affecting a single sex
Trisomy testing
Occasionally chromosome deletions or single gene deletions
If NIPT shows + for Down’s syndrome, what would be the next line investigation?
Amniocentesis
Once foetal DNA has been extracted from maternal blood in NIPT, what should be done with it to get infomation?
What factors may increase the risk of false positives?
Array CGH
Mother having breast/ovarian cancer, lab error, mosaicism
Mrs Pink comes to see you. She is 10 weeks pregnant. She has a son who is affected with DMD. What is the first test that you should do?
If this shows the sex is female, what is the management?
If this shows the sex is male, what is the management?
NIPT
Nothing, the child will be fine
Chorionic villus sampling (there is a 50/50 chance the child will be affected)
Mrs Green is 12 weeks pregnant – serum biochemistry and nuchal thickness measurement gives a risk of 1 in 40 that the baby is affected with Down’s Syndrome. What is the first test that you should do?
NIPT (as a screening test)
Mrs Blue comes to see you. She is 18 weeks pregnant. A detailed scan has shown that her baby has a cardiac defect, an ASD which is commonly seen in Down’s Syndrome. What is your best genetic management?
What is the best first genetic test that you would do with the DNA extracted from the previous test?
Amniocentesis (already got a known structural abnormality, and is at the appropriate gestation)
Array CGH
Array CGH will only pick up what?
What is a Robertsonian translocation?
Robertsonian translocations increase the risk of what?
Unbalanced chromosome abnormalities
Two acrocentric chromosomes stuck end to end
Trisomy in a pregnancy
What is trisomy 21? What is the outcome?
What is trisomy 18? What is the outcome?
What is trisomy 13? What is the outcome?
Down’s syndrome - generally happy children with a reasonable life expectancy but lots of health conditions
Edward’s syndrome - often die in utero, only survive for short periods of time
Patau’s syndrome - often miscarry, or if survive only live for a month
