1. Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada.
2. Departments of Biology and Paediatrics, Queen's University, Kingston, Ontario K7L 3N6, Canada.
3. Department of Medical Genetics, Oregon Health Sciences University, Portland, OR 972611.
4. Paediatric Genetics Unit, Institute of Child Health, London, WC1N1EH, England.
5. Booth Memorial Medical Center, Flushing, NY 11355.
6. Laboratoire de Cytogenetique, Centre Hospitalier, Chambery, France.
7. Institute of Medical Generics, University of Zurich, Zurich, Switzerland.
8. Genetics Department, Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.