Down Syndrome Flashcards
Women, irrespective if age, are offered a screening programme for down syndrome in which trimester of pregnancy?
First trimester
Describe the tests involved in the Down Syndrome screening progamme.
Nuchal translucency measured by ultrasound
Blood test for pregnancy associated gonadotrophin-A (PAPP-A) and free beta human chorionic ginadotrophin
If a foetus were ti test positive for Down syndrome on a screening test, what would the results be for each of the three tests?
NT thickness increased
PAPP-A decreased
FbetahCG increased
These scores combined with maternal age would give a 1 in 150 chance of down syndrome to meet the cut off
If a screening test for Down syndrome was positive, what are the two possible tests which would next be done to confirm diagnosis?
Amniocentesis
Chorionic villus sampling
Describe the new method of screening for down syndrome - non-invasive prenatal testing.
Cell fre DNA - DNA fragments in the maternal plasma would be analysed following a blood sample from the mother.10-20% of the cell-free DNA would be from the embryo and the DNA fragments would be mapped. Down syndrome babies would have more chromosome 21 than expected
Most cases of down syndrome result from trisomy 21. How can this occur?
This arises from non-disjunction, usually at the first but sometimes at the second meiotic division.
Non-disjunction is where there is a failure of paired chromosomes or sister chromatids to disjoin at anaphase.
Is it more likely for the mother or the father to contribute the extra chromosome, in trisomy 21?
Mother
In terms of Down sydrome, what is mosaicism, and how does this present differently to other cases of down syndrome?
In mosaicism, the person will have some normal cell lines and some trisomy 21 cell limes resulting in milder clinical symptoms that other patients with down syndrome
In a small number of cases, down syndrome is not caused by non-disjunction or mosaicism. In this case, how does the child receive an extra chromosome 21?
They may have recieved an extra chromosome from a parent who is a carrier of a balanced robersonian translocation involving chromosome 21
What is meant by ‘a balanced translocation’?
A translocation is the transfer of chromosomal material between chromosomes. This exchange usually results in no significant kiss of DNA and no gene disruption and the individual, is therefore, usually clinically normal and so is said to have a balanced translocation
Is it possible for people with down syndrome to reproduce?
Men with down syndrome are infertile but there have been cases where women with down syndrome have had children
What are the risk factors for down syndrome?
Increasing age of mother
Previous sibling with down syndrome
Abnormal parental karyotype with a translocation
Describe the fascial features of a person with down syndrome?
Palpebral fissure upslanting Bushfield spots Small nose Flat fascial profile Low set ears Brachycephalic skull
Puberty is often delayed or incomplete in individuals with down syndrome. What height may these people grow to?
150cm
People with down syndrome will commonly have learning disabilities. Their IQ is usually less than…?
50
