Topic 2: Genetic screening Flashcards
Key Summary: What are the uses of genetic screening?
4 uses
- To confirm diagnosis of a genetic disease
- Identification of carriers
- Pre-implantation genetic diagnosis – screens IVF EMBRYOS
- Pre-natal testing - {chorionic villus sampling/CVS}, amniocentesis or NIPD – screens FETUS OR FETAL DNA
Describe the process of confirming diagnosis of a disease using genetic screening.
(2 steps)
- {White blood/cheek} cell sample taken - both easy to collect and diploid so contain larger quantity of DNA.
- DNA extracted and tested for presence of {defective/mutated} allele (confirms that they have the disease).
NOTE: Usually used to screen new-born babies to confirm they have a genetic disease when symptoms are observed
Describe the process of identifying carriers using genetic screening (pre-conception or confirmation of diagnosis screening). (2 steps)
At what stage of life can this be done? (1 point)
- {White blood/cheek} cell sample taken - both easy to collect and diploid so contain larger quantity of DNA.
- DNA extracted and tested for presence of {defective/mutated} gene – compare with normal DNA sequence.
- this can be done at any stage of life after birth
Describe the process of pre-implantation genetic diagnosis (PGD/PIGD) using genetic screening.
(4 steps)
- Eggs fertilised by sperm in the lab to create zygotes
- Allowed to divide to 8 cell embryo stage, then one cell removed
- DNA extracted and tested for presence of the defective allele
- Only embryos without the {recessive CF allele / defective allele} are implanted into uterus
NOTE: Used only during IVF
Name the 3 types of pre-natal (before birth) screening
3 types
- Amniocentesis
- Chorionic villus sampling (CVS)
- Non-invasive prenatal diagnosis (NIPG)
Describe the process of {non-invasive prenatal diagnosis/NIPD}
(2 steps)
At what “age” of the pregnancy is this done at? (1 point)
- ANALYSES CELL FREE DNA (cffDNA) from mother’s blood plasma during pregnancy
- DNA can be analysed to detect defective {gene/mutation}
- this is done at 7-9 weeks
What are the 2 advantages of {non-invasive prenatal diagnosis/NIPD}? (2 advantages)
- no risk of miscarriage
2. can be done earlier than Chorionic villus sampling (CVS) and amniocentesis so that an early abortion is possible
Describe the process of Amniocentesis
(4 steps)
At what “age” of the pregnancy is this done at? (1 point)
- Baby’s position determined by ultrasound
- Needle inserted through abdomen into uterus
- Small volume of AMNIOTIC FLUID WITH FETAL CELLS removed
- DNA in cells analysed to detect defective allele
- Done at 15-17 weeks
NOTE: takes 1 hour, results in a day
Describe the process of Chorionic Villus Sampling
(4 steps)
At what “age” of the pregnancy is this done at? (1 point)
- Baby’s position determined by ultrasound
- Needle inserted through abdomen or cervix into uterus
- Small amount of PLACENTA (contains fetal cells) is removed
- DNA can be analysed to detect defective allele
- Done at 8-12 weeks
NOTE: takes 1 hour, results in a few days
Key Summary: {What are the {benefits/advantages} of testing (genetic screening)/why would some people choose to be tested}?
(4 points)
- Gives information about abnormalities in {fetus/DNA}
- Allows {people to make informed decisions / opportunity for choice / people to consider a termination (abortion)}
- Information allows people to {{prepare/research treatment} / start counselling}
- Gives the choice of IVF – to implant only embryos without the gene mutation
Key Summary: Disadvantages of testing (genetic screening)
3 disadvantages
- Tests may not be 100% accurate, leading to false negative or positive result – so decisions based on false info
- Screening does not test for all the possible mutations that can cause cystic fibrosis
- Other genetic abnormalities {may be found/may cause further stress}
Key Summary: Why would some people choose NOT TO BE tested? (genetic screening)
(3 points)
- Increased risk of procedure causing a miscarriage so potentially a healthy fetus would be lost.
OR
- Test result may be inaccurate (false positive/negative) so false positive may lead to abortion of a healthy fetus.
OR
- {Prenatal testing / abortion} may be against values or beliefs of parents
Key Summary: What are the ethical issues relating to the use of prenatal testing?
(5 issues)
- foetus is living – potential human being
- positive test result may result in a choice of abortion
- {who has the right to make the decision for the foetus? / FOETUS HAS {DECISION RIGHTS/RIGHT TO LIFE}}
- it is unethical to {cause the death of a foetus / destroy a potential human being} – it is {wrong / murder} – foetus has a right to live
- RISK OF FALSE NEGATIVE OR FALSE POSITIVE (If false positive - healthy fetus could be aborted. If false negative – parents would not be prepared for a child with a genetic disease)
What are the social issues relating to the use of prenatal testing?
(8 issues)
- who has right to decide if tests should be performed
- implications of {medical costs /disagreements} over next step
- some other abnormality may be found
- possible problems with {future employment / insurance}
- parents may not fully understand possible risks of prenatal testing
- possibility of miscarriage or harm to child – healthy child could be lost
- confidentiality issues for {parents / child}
- {some other abnormality may be found / paternal DNA does not match / do other family members have right to know results?}
When is pre-conception or confirmation of diagnosis screening performed? (1 point)
- From birth onwards
