[1] Washington Univ, Dept Pediat, Sch Med, St Louis, MO 63110 USA
[2] UCL Inst Child Hlth, Neurosci Unit, London, England
[3] Case Western Reserve Univ, Ctr Clin Invest, Cleveland, OH 44106 USA
[4] Case Western Reserve Univ, Dept Pediat, Cleveland, OH 44106 USA
[5] Washington Univ, Div Biostat, Sch Med, St Louis, MO 63110 USA
[6] St Marys Hosp, Imperial Coll Healthcare Natl Hlth Serv Trust, Dept Haematol, London, England
[7] Great Ormond St Hosp Sick Children, Dept Cardiol, London WC1N 3JH, England