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

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

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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%

answered Apr 28, 2014 by Sujit Shrestha Medical Officer (1,796 points)