[1] Univ Washington, Sch Med, Seattle, WA 98195 USA
[2] Univ Toronto, Toronto, ON, Canada
[3] Univ Rochester, Sch Med & Dent, Rochester, NY USA
[4] Northwestern Univ, Chicago, IL 60611 USA
[5] Erasme Univ Hosp, B-1070 Brussels, Belgium
[6] Kings Coll Hosp London, London, England
[7] Abbott Labs, Abbott Pk, IL 60064 USA