A parent's guide to the genetics of Down syndrome.

Down syndrome is a genetic disorder, occurring when an individual has all or part of an extra copy of chromosome 21. Parents of children with Down syndrome are often confused by the term genetic disorder because they associate the term with inheritance but have also learned that Down syndrome is not typically inherited. These parents may have questions about the nature of chromosomes, how Down syndrome occurs, recurrence risk and more. This article attempts to address many of the common questions parents of children with Down syndrome express regarding the genetics of the disorder including the mechanisms by which Down syndrome occurs: nondisjunction, translocation and mosaicism, as well as providing information about prenatal testing options, how the diagnosis is made and where parents may go for further information.