Lettrt To The Editor

Our comments on the discordance of leukemia in monozygotic (MZ) twins were based on the assumption that such twins have an identical genome, at least prior to a leukemogenic event. Dr. Feehan correctly points out that this view requires some qualification. Although cytoplasmic inheritance may contribute to differences between MZ twins, asymmetry of implantation and circulation as well as somatic mutation and chromosal defect may also lead to discordance in the expression of a disorder.1,2