Chromosomal Abnormalities Flashcards
Name 3 examples of trisomies.
- Down syndrome (most common)
- Edwards syndrome (2nd most common)
- Patau syndrome (3rd most common)
What causes Down syndrome?
- Usually free standing trisomy 21.
- Can also result from unbalanced Robertsonian translocation.
What are the symptoms of Down syndrome?
- Intellectual disability
- Hypotonia (lack muscle tone)
- Characteristic facial features
- Heart defects
What are the health consequences of Down syndrome?
- Increased prevalence of leukaemia
- Increased incidence of early Alzheimers’
What are the causes of Edwards’ syndrome?
- Usually free-standing trisomy 18
- Involves maternal meiosis II error
What are the symptoms of Edwards syndrome?
- Antenatal growth deficiency
- Specific craniofacial features:
- small lower jaw
- low-set ears - Major systems malformations
- rocker bottom feet
- overlapping fingers - Cognitive developmental delay
What is the modal lifespan in Edwards syndrome?
5-15 days
In which gender is Edwards syndrome more prevalent?
Females
What are the causes of Patau syndrome?
- Usually free standing trisomy 13
- Can also result from unbalanced Robertsonian translocation
What are the symptoms of Patau syndrome?
Multiple congenital abnormalities, e.g. Polydactyly and holoprosencephaly (brain doesn’t divide in 2 halves, can present with cleft lip)
What is the lifespan in Patau syndrome?
Majority die in neonatal period
Name an example of a monosomy.
Turner syndrome (45,X)
What are the symptoms of Turner syndrome?
- Short stature (monosomic for SHOX gene)
- Mild learning difficulties
- Infertility
- Neck webbing
Why is the loss of an X chromosome problematic?
- X and Y chromosomes have short regions in common (PAR1 and PAR2 pseudo-autosomal regions) at the tips of the short and long arms, allowing for pairing during cell division.
- Turner patients will be monosomic for genes in the PARs, e.g. SHOX gene associated with short stature.
