Genetics/PGT Flashcards
When might a clinical geneticist be required in pregnancy?
Family history that can affect the pregnancy
Unexpected finding in pregnancy
Previous pregnancy/child has genetic issues
Genetic testing available in pregnancy?
Chorionic villous biopsy
Amniocentesis
Non-invasive pre-natal testing
What gestation can chorionic villous biopsy be done in pregnancy?
11.5 weeks
Possible problem with chorionic villous biopsy for picking up genetic problems?
Risk of confined placental mosaicism - this is when the placenta has different cells than the baby does
What is confined placental mosaicism?
The placenta has different cells than the baby does
What week gestation can you do amniocentesis?
15+ weeks
What week gestation can you do non-invasive pre-natal testing?
8+ weeks
What can non-invasive pre-natal testing be used for?
trisomy testing
sex determination for x-linked disorders
What does non-invasive pre-natal testing test?
Free foetal DNA in the maternal circulation
What is usually the first line genetic analysis test used if there is a problem found in pregnancy?
Chromosome microarray (i.e. arrayCGH)
What does arrayCGH do?
Looks at chromosomes and spots imbalances (i.e. extra or missing things)
What is a potential problem when using a whole genome test?
It will also pick up polymorphisms instead of just mutations
When would chromosomal analysis be required?
High risk of chromosomal trisomy
Foetal abnormality on scanning
Parent has a balanced chromosomal rearrangement
What prenatal screening is there in Scotland?
12 weeks - dating US scan and serum biochemistry
16 weeks - serum screening
20 weeks - detailed scan to look for other foetal abnormalities
What is pre-implantation genetic testing?
A test performed to analyse the DNA from oocytes or embryos for HLA typing or for determining genetic abnormalities
What is the most common thing that is tested in PGT?
Blastocyst
Why is the embryo frozen after it undergoes PGT?
To allow time for the test to be carried out
What are the 3 categories of PGT?
PGT-A (aneuploidy)
PGT-SR (structural rearrangements)
PGT-M (monogenic)
PGT-A is a diagnostic/screening test?
Screening
PGT-SR is a diagnostic/screening test?
Diagnostic
PGT-M is a diagnostic/screening test?
Diagnostic
What does PGT-A do?
Screens for presence of all 23 pairs of chromosomes
What does PGT-SR do?
Detects translocations, inversions and deletions
What does PGT-M do?
Detects known inherited disorders
Examples of conditions that may be picked up on PGT-M?
Thalassaemia
Sickle cell anaemia
Haemophilia
CF
Huntington’s disease
Fragile X syndrome
BRCA mutations
Indications for PGT-A use?
Advanced maternal age
Recurrent implantation failure
Recurrent miscarriages
Severe male factor infertility
What is the primary purpose of a screening test?
detect early disease or risk factors for disease in large numbers of apparently healthy individuals
What is the purpose of a diagnostic test?
to establish the presence of disease as a basis for treatment decisions in symptomatic or screen positive individuals
