1. Departments of Obstetrics and Gynecology, Human Genetics and Development, College of Physicians and Surgeons, Columbia University New York 10032, U.S.A.
2. M.R.C. Population Genetics Unit Old Road, Headington, Oxford, England
3. Department of Tumor Biology, Karolinska Institutet S-104 01 Stockholm 60, Sweden
4. Sir William Dunn School of Pathology, University of Oxford Oxford, England