[1] Univ Toronto, Toronto Gen Hosp, Hemoglobinopathy Res Program, Toronto, ON M5G 2C4, Canada
[2] Univ Oxford, John Radcliffe Hosp, Weatherall Inst Mol Med, Oxford OX3 9DU, England
[3] Univ Kelaniya, Fac Med, Colombo, Sri Lanka
[4] John Radcliffe Hosp, MRC, Mol Hematol Unit, Oxford OX3 9DU, England