Genetics

Question 1

A woman who is 12/40 pregnant attends a booking clinic. She wants to know the options for Down’s screening. What are the 2 options and what results would suggest increased risk of Down’s?

Answer 1

1. Combined test at 11+0 to 13+6
   - nuchal translucency: increased
   - free B-hCG: increased
   - PAPP-A: decreased
2. Serum screen at 15+0 to 20+0
   - free B-hCG: increased
   - AFP: decreased
   - unconjugated estriol: decreased
   - inhibin-A: increased

Question 2

A pregnant woman finds out from her Down’s screening test that her pregnancy is high risk (>1/150). How could diagnosis be confirmed?

Answer 2

1. chorionic villus sampling (11 to 14 wks)

2. amniocentesis (>15 wks)

Question 3

A male baby is born at term. He is diagnosed with Down syndrome. Which features are characteristic of this condition?

Answer 3

• generalised hypotonia
• small stature
• flattened occiput
• small low set ears
• upslanting palpebral fissures + epicanthal folds
• flat nasal bridge
• protruding tongue
• excess nuchal skin
• single palmar crease (Simian)
• brachydactyly
• clinodacytly
• ‘sandal gap’ between 1st and 2nd toes
• intellectual impairment

Question 4

What is the most common CHD in babies with T21?

Answer 4

atrioventricular canal defect

Question 5

A mother who has received no antenatal care gives birth to a baby with microcephaly and polydactyly. What is the diagnosis?

Answer 5

Patau syndrome (T13)

Question 6

A mother who has received no antenatal care gives birth to a baby with rocker-bottom feet and overlapping fingers. What is the diagnosis?

Answer 6

Edward’s syndrome (T18)