Genetic Conditions

Question 1

What is Down syndrome?

Answer 1

trisomy 21
* Genetic condition where they have an extra copy of chromosome 21
* Mainly caused by nondisjunction (chromosomes don’t split apart during meiosis so there are cells that have double and cells that have no chromosomes at the end)
* One of the most common chromosomal disorders

Question 1

What is Down syndrome?

Answer 1

trisomy 21
* Genetic condition where they have an extra copy of chromosome 21
* Mainly caused by nondisjunction (chromosomes don’t split apart during meiosis so there are cells that have double and cells that have no chromosomes at the end)
* One of the most common chromosomal disorders

Question 2

What is the strongest risk factor for Downs syndrome

Answer 2

• Maternal age is the strongest risk factor for Down’s syndrome, older the mother, the higher the risk

Question 3

Physical and health features of Downs?

Answer 3

• Physical features include: flat facial profile, almond shaped eyes, single palmar crease, wide short hands and fingers, widely separated first and second toe, small ears and mouth, excess skin at the nape of the neck, Brushfield spots on the eye (white spots slightly elevated on the iris)
• Health features: hypotonia, Atrial septal defects in the heart, duodenal atresia, increased risk of ALL, sterility in males, intellectual disability and increased risk of Alzheimers

Question 4

First feature often noticed when a baby with Downs is born?

Answer 4

hypotonia

Question 5

Describe antenatal trisomy screening?

Answer 5

• In Down’s syndrome (T21) it is difficult to predict how the baby might be affected and there is a spectrum
• Edward’s (T18) and Patau’s (T13) if complete are likely to be lethal
• Trisomy risk assessment in the first trimester involves measuring nuchal translucency and combined with HCG and PAPP-A blood test to give a risk level that the baby has Down’s
• This combination detects up to 90% of T21 with 5% false positive rate
• Second trimester screening can also be done but only for T21, whereas in first trimester can screen for T18 and T13 as well
• Non-invasive prenatal testing (NIPT) detects fetal DNA fragments in a sample of blood taken from the mother and is more accurate than the combined test so can be offered to women identified as high risk from the combined test (not offered first because it’s more accurate in those already identified as high risk), it is STILL only a screening test (so you can’t offer TOP based on result but stops women who don’t need an invasive test having one)
• Women who have high risk combined test and NIPT may then go on to have diagnostic testing

Question 6

Describe diagnostic testing for Downs?

Answer 6

• Diagnostic tests can be done for a range of conditions including trisomy 21
• Amniocentesis is done after 15 weeks, miscarriage rate is < 1%
• Chorionic villus sampling is done after 12 weeks, miscarriage rate is < 2%

Question 7

Describe phenotype for Digeorge syndrome?

Answer 7

22q11 deletion
cleft lip or palate
hypoparathyroidism
learning difficulties
short stature
primary immunodeficiency - may have absent thymus
aortic arch defects

Question 8

Turner’s syndrome phenotype?

Answer 8

Presence of only 1 X
short statue, shield chest/ wide spaced nipples, webbed neck, bicuspid aortic valve, coarctation of the aorta, primary amenorrhoea with hypergonadotrophic hypogonadism