[1] Mem Univ Newfoundland, Div Clin Genet, Dept Med, St John, NF A1B 2V6, Canada
[2] Mem Univ Newfoundland, Patient Res Ctr, St John, NF A1B 2V6, Canada
[3] Mem Univ Newfoundland, Dept Med, Div Haematol, St John, NF A1B 2V6, Canada
[4] Mem Univ Newfoundland, Dept Med, Clin Epidemiol Unit, St John, NF A1B 2V6, Canada