A t(5p-;21q+) translocation in a family with Down syndrome.

A mother and daughter carrying a t(5;21)(p13;q22) chromosome were discovered after they had contacted us for genetic counseling. They were concerned because of two cases of Down syndrome in their family. Four of the mother's eight pregnancies had resulted in miscarriages; the chromosome complements of the abortuses is not known. Evidence was found indicating that individuals carrying a structurally altered chromosome 21 have an increased risk of bearing a child with Down syndrome.