A new stable human dicentric chromosome, tdic(4;21)(p16;q22), in a woman with first trimester abortion.

A woman with first trimester abortion and a dicentric chromosome formed from a 4 and a 21 is described. The dicentric chromosome was stable and in the majority of cells the 21 centromere was active, while in a minority the chromosome 4 centromere was active. This shows that both centromeres were functional, but that only one functioned in any given cell. Suppression of the activity of one centromere might be the mechanism by which this dicentric chromosome achieved its stability. A dicentric formed from a chromosome 4 and a 21 has not apparently been previously reported.