Down's Syndrome: Epidemiology and Genetics

Question 1

What is the risk of having a baby with Down’s Syndrome at 20 years of age?

Answer 1

1 in 1,500

Question 2

What is the risk of developing Down’s Syndrome at 30 years of age?

Answer 2

1 in 800

Question 3

What is the risk of developing Down’s Syndrome at 35 years of age?

Answer 3

1 in 270

Question 4

What is the risk of developing Down’s Syndrome at 40 years of age?

Answer 4

1 in 100

Question 5

What is the risk of developing Down’s Syndrome at 45 years of age?

Answer 5

1 in 50 or greater

Question 6

What is an easy way to remember the risk of developing Down’s syndrome by age?

Answer 6

Start at 1 in 1,000 at 30 years of age.

Then divide the denominator by 3 for every 5 years.

1 in 1,000 at 30 years.

1 in 300 at 35 years.

1 in 100 at 40 years.

1 in 33 at 45 years.

Question 7

What is the most common cytogenetic cause of down’s syndrome?

Answer 7

Non-disjunction (94%)

Question 8

What is the risk of a mother < 35 years having another child with down’s syndrome if the mode of mutation is non-disjunction?

Answer 8

1 in 100 if mother < 35 years.

Question 9

What are the other cytogenetic forms of mtuation?

Answer 9

1. Robertsonian translocation
2. Mosaicism