[1] Univ Sheffield, Sch Med, Div Genom Med, Sheffield S10 2RX, S Yorkshire, England
[2] Imperial Canc Res Fund, Genet Epidemiol Div, Ctr Clin, Leeds, W Yorkshire, England
[3] Univ Dundee, Ninewells Hosp & Med Sch, Ctr Biomed Res, Dundee DD1 9SY, Scotland