Does Down syndrome run in families?

All three types of Down syndrome are genetic conditions (relating to the genes), but only one percent of all cases of Down syndrome have a hereditary component (passed from parent to child through the genes). Heredity is not a factor in two types of Down syndrome, trisomy 21 (nondisjunction) and mosaicism. Translocation, a type of Down syndrome that accounts for three to four percent of all cases, is the only type of Down syndrome known to have a hereditary component. Of those, one-third (or one percent of all cases of Down syndrome) are hereditary.

The age of the mother does not seem to be linked to the risk of translocation; most cases are sporadic, chance events. However, in about one-third of cases, one parent is a carrier of a translocated chromosome.

This content originally appeared on the National Down Syndrome Society website.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.