[1] Alberta Childrens Prov Gen Hosp, Dept Med Genet, Dept Genet, Calgary, AB T2T 5C7, Canada
[2] Natl Ctr Radiobiol & Radiat Protect, Sofia, Bulgaria
[3] Univ Calgary, Fac Med, Dept Obstet & Gynecol, Calgary, AB T2N 4N1, Canada
[4] Northwestern Univ, Sch Med, Ctr Canc, Biometry Sect, Chicago, IL 60611 USA
[5] Univ Calgary, Fac Med, Dept Med Genet, Calgary, AB T2N 4N1, Canada