[1] Univ Wales Hosp, Inst Med Genet, Dept Cytogenet, Cardiff CF4 4XW, S Glam, Wales
[2] Univ Wales Coll Cardiff, Coll Med, Inst Med Genet, Cardiff CF1 3NS, S Glam, Wales
[3] Univ Wales Coll Cardiff, Coll Med, Dept Pathol, Cardiff CF1 3NS, S Glam, Wales
[4] Imperial Canc Res Fund, Mol & Populat Genet Lab, London WC2A 3PX, England