1. Departments of Physiology (N.M.M., J.F.M., C.A.W., M.J.S.), St. Georges Hospital Medical School, London, United Kingdom SW17 0RE
2. Medical Genetics (N.D.C.), St. Georges Hospital Medical School, London, United Kingdom SW17 0RE
3. Department of Veterinary Basic Sciences, Royal Veterinary College (R.J.S.), London, United Kingdom NW1 0TU