MCGB - Chromosome Abnormalities Flashcards
What is cytogenetics?
Study of the genetic constitution of cells through the visualisation and analysis of chromosomes
Give some reasons for cytogenetic analysis to be carried out.
- accurate diagnosis/prognosis of clinical problems
- better clinical management
- assess future reproductive risks
- prenatal diagnosis
What are “constitutional abnormalities”?
They are a reason for referral for cytogenetic analysis - includes prenatal diagnosis, birth defects, infertility etc
What are “acquired abnormalities”?
Also referral reason for cytogenetic testing - include leukaemias, solid tumours etc
Give two prenatal diagnosis methods.
- chorionic villus sampling (11-12 weeks, 1.2% miscarriage risk)
- amniocentesis (15+ weeks, 0.8% miscarriage risk)
Give some examples of birth defects that can be identified by prenatal screening.
Dysmorphism, congenital malformations, mental retardation, developmental delay, specific syndromes (eg. Downs, Williams, DiGeorge)
What is the name of this procedure?
Metaphase chromosomes are stained, paired up and grouped together. Abnormalities are identified and described.
Karyotyping
Give an example of a disorder caused due to trisomy.
Down’s syndrome (+21), Patau syndrome (+13), Edwards syndrome (+18)
Give a disorder caused by monosomy.
Turner syndrome (only one X)
What is polyploidy?
Gain of a whole haploid set of chromosomes, like trisomy but for entire set of chromosomes. Usually spontaneously aborts during pregnancy.
What is the most common cause of polyploidy?
Polyspermy - fertilisation of an egg by more than one sperm.
What is it called when chromosomes are “left behind” at cell division due to defects in spindle function?
Anaphase lag
What is Edwards syndrome?
Trisomy 18. Usually only live 5-15 days, symptoms are rocker bottom feet, low-set ears, overlapping fingers, small lower jaw.
What does trisomy 13 cause?
Patau syndrome
What is Turner syndrome?
Occurs when girls are born with one functioning X chromosome. Symptoms include puffy feet, redundant skin at back of neck, short stature
What is mosaicism?
Presence of 2 or more cell lines in an individual, usually caused by mitotic non-disjunction.
Give some examples of cytogenetic structural abnormalities.
- translocations
- inversions
- deletions
- duplications
- insertions
What are reciprocal translocations?
Exchange of material between two chromosomes, eg part of chromosome 4 breaks off and is swapped with part of chromosome 18.
What is a Robertsonian translocation?
Participating chromosomes break at their centromeres and the long arms fuse to form a single, large chromosome with a single centromere.
What is the benefit of using a whole chromosome paint?
Can identify individual chromosomes even when they are rearranged.
What does microarray comparative genomic hybridisation do?
Examines the whole genome at high resolution, comparing normal control DNA to patient DNA.
Give an anvantage and a disadvantage of array CGH.
+ examines entire genome
+ targeted against known genetic conditions
- more expensive than karyotyping
- does not detect balanced re-arrangements
