What is the risk of other baby having down syndrome if one already has it?

Question

If One baby has down syndrome, what is the risk of the other baby having down syndrome?

Answer 1

**First of all we need to know the cause of down syndrome-**
1. Non-dysjunction that occurs in 95% cases
2. Translocation- 4%
3. Mosaicism- 1%

For a non-dysjunction recurrence risk is same as the population for that maternal age.

For Translocations- t(21:21) in parents is associated with 100% recurrence of down syndromein subsequent pregnancy.
    t(4:11) is associated with 5-7% recurrence rate

If a mother has Down Syndrome, she can still be fertile and able to reproduce, with chance of having a baby with downsyndrome by 50%