Genetics Flashcards
(41 cards)
How is Down’s syndrome screened for?
- Nuchal Translucency (skin fold thickness behind neck)
- Blood serum markers in mother
Why is the nuchal translucency increased in babies with Down’s Syndrome?
- indication that lymphatics are developing too slowly
=> gap is too large
How is invasive genetic testing done whilst the foetus is in utero?
- need to test tissue with same genetic makeup as the baby
i. e. chorionic villus sampling of placenta OR amniocentesis
When can chorionic villus sampling and amniocentesis take place?
CVS - 11.5 weeks
Amniocentesis - 15 weeks
What is Non Invasive Prenatal Testing?
Taking mothers blood and testing for free foetal DNA
- this can get into mothers circulation via placenta
What can non-invasive prenatal testing look for?
- sex of baby
- trisomy
OCCASIONALLY
- chromosome deletions
- single gene transfers
What is meant by confined placental mosaicism?
- trophoblasts divide quickly => develop more abnormalities than cells that go on to become blastocyst
=> Placenta may have chromosome abnormalities that the baby does NOT have
If NT, serum markers in the mothers blood and NIPT indicate a high risk of Trisomy 21, what is the percenatge risk of the baby having this condition?
99%+
How do geneticists test mothers blood in NIPT and confirm a high suspicion of trisomy 21?
- count number of each chromosome i.e. 1,2,3 etc
- Count number of chromosome 21
=> if out of proportion to number of other chromosomes, this would indicate T21
NIPT can also be used for what other genetic conditions?
T18 (Edward’s)
T13 (Patau’s)
Also Turners 45X and Kleinfelters 47XXY
What does NIPT reduce the risk of?
Miscarriage due to amniocentesis
Describe the appearance of a baby with Down’s Syndrome ?
- short fingers
- round face
- large tongue
- epicanthic folds
What are the benefits of an antenatal genetic screening test?
- identify and treat early
- identify if other family members are at risk
Why is there a debate surrounding screening for Down’s Syndrome in pregnancy?
- there is not additional benefit to treating early
- HOWEVER people do say that early termination option for mother may be a benefit to the child
Up to what gestation can a mother choose to terminate her baby who is at risk of down’s syndrome?
NO LIMIT
- if risk of serious abnormality to child or to health of the mother
WHat is anencephaly, and why is early diagnosis significant?
- no brain/head development
- baby MAY progress to full term (may be stillborn due to labour)
- parents need to psychologically prepare for appearance and limited survival of baby
If a family do not wish to proceed with a termination after a difficult genetic diagnosis in their baby, what other option do they have?
- carry baby to term
- organ donation
How does a baby with T18 (Edward’s) appear, and how long do babies with this condition survive?
- small baby with smal facial features
- life limited => many don’t survive for long after birth (virtually none within 1 year)
Is Down’s Syndrome considered a “severe” genetic disease?
- Not necessarily due to variable presentation
- parents may not be equipped do deal with any of these
They can have:
- cardiovascular disease
- behaviour issues
- low IQ requiring lots of support
- multiple surgeries -> time in ICU
- increased incidence of some cancers
If a US scan indicates a hand abnormality, what must you be aware of?
- is this part of another condition/syndrome?
- e.g. DiGeorge, Thrombocytopaenic Absent Radius etc
What criteria do patients make a Termination of Pregnancy decision upon?
- social/religious views
- previous experience
- perception of disease
What is NIPT eventually going to be able to analyse?
Chromosome Karyotype
What invasive genetic testing is carried out on the chorionic villus sample of on an amniocentesis sample?
- Chromosome Microarray (1st Line)
- Single Gene changes
=> PCR
=> Next Generation Sequencing
What is the problem with chromosome microarray?
Cannot pick up balanced translocations
- only identifies EXTRA or MISSING genetic material
