Week 2 Flashcards
(41 cards)
What is aneuploidy
Abnormal number of chromosomes in a haploid set
Clinical features in the newborn period
Hypotonia
Sleepiness
Excess nuchal skin
Craniofacial clinical features of DS
Brachycephaly - shorter skull
Epicanthic folds - skin fold of the upper eye covering the inner eye corner
Protruding tongue
Small ears
Upward sloping palpebral fissures
Strabismus - eyes point in diff directions
Clinical features of DS in limbs
Single palmer crease
Small middle phalanx on the fifth finger
Wide gap between first and second toes
Clinical features of DS - cardiac
Atrial and ventricular septal wall defects
Common AV canal
Patent ductus arteriosus - persistent opening between two blood vessels leading from the heart
What is atresia in DS
narrowing
Anal atresia and duodenal atresia are clinical features of DS
What is hirschsprung disease
Stool stuck in bowels
A clinical feature of DS
IQ in DS children
Have a broad range
25-75
Normal - 40-45
Social skills in DS children compared to normal
Relatively happy, advanced and affectionate
Average height in DS patients
150 cm
Life expectancy in DS patients
50-60 years
15-20% of heart affected DS patients have an early death
Alzheimer’s relation to DS
Early onset Alzheimer’s is common in DS patients - 2-3 decades earlier
Development of Alzheimer’s
- Shrinkage of cerebral cortex + enlarged ventricles
- Amyloid beta plaques
- Tau neurofibrillary tangles
- Amyloid precursor protein
How does amyloid precursor protein contribute to Alzheimer’s
Beta and gamma- secretase abnormally cleave onto APP
Which generates beta amyloid peptides
Which accumulate into neurotoxic amyloid plaques in the brain tissues
What is the main chromosomal cause of DS
Meitotic non-disjunction (90%)
- error in cell division meiosis 1
- causes trisomy in chromosome 21
- mechanism = one chromosome pair fails to split into two
Other chromosomal causes of DS
- mitotic non-disjunction
- robertsonian translocation
What is screening
Test applied to a whole population
Identifies those at high risk
What is a diagnostic test
More specific test that identifies those who have the disease
How does screening in DS work
Pregnant women are offered a screening test
Using an algorithm a probability is calculated
If P > 1/150, a diagnostic test is offered
What are the methods of screening used for DS
- Ultrasound
- Serum markers
- Cell free foetal DNA
- Non invasive prenatal testing
How is ultrasound used for DS
Identifies the nuchal translucency feature
What bio markers are used for serum marker screening test used for DS screening
2 bio markers are used
- low pregnancy associated plasma A
- high human chorionic gonadotropin hCG
How are serum markers used to screen DS
Quadruple test
1. Decreased alpha fetoprotein
2. Decreased unconjugated estriol
3. Elevated hCG
4. elevated inhibit A
Triple test - inhibit A is not included
P>1/150 - diagnostic test is offered
mitotic non-disjunction
failure of two chromosomes to separate during mitosis
so both go to one daughter cell
