Reproduction in a woman with low percentage t(21q21q) mosaicism.

Abstract
The birth of a child with Down syndrome followed by the conception of a fetus, both bearing the t(21q21q) chromosome in 100% of their cells, is described for a woman mosaic for the translocation in less than 10% of 2 of her examined tissues and in none of the cells in her peripheral blood. The importance of examining as many parental tissues as possible for the detection of low percentage mosaicism is stressed.