Supernumerary chromosome inherited from a maternal balanced translocation leading to pure trisomy 9p

We describe a child with a supernumerary chromosome defined as der(9)t(9;22 ) (q12;p11), resulting in trisomy 9p and trisomy 22p, The mother carried th e balanced translocation. In G- and C-banding the derivative chromosome 9 a ppeared to be dicentric and to contain 22q material. Using in situ hybridiz ation we defined the exact breakpoints of the translocation and ruled out t he possibility of a centric fission in the mother's chromosomes. (C) 2000 W iley-Liss, Inc.