In Utero Events

Toxic exposure in utero to maternal Epstein-Barr virus (EBV) reactivation or other viral entities such as cytomegalovirus and herpes simplex virus has been proposed as a causative factor in some infants and children with ALL.37 These mutations are not believed to lead directly to ALL, but their effect in delaying cell maturation may allow more genetic abnormalities to occur.10

Monozygotic twins carry a small but definite increased risk of concordant ALL. The potential for in utero events leading to postpartum ALL was highlighted in a report of two year-old monozygotic twins, both with ALL, in whom one had two rearranged T-cell receptor 8 alleles that were proposed to have occurred in utero, with the transmission of a single allele to the other twin, resulting in ALL.38 Though these changes were considered critical, other abnormalities or mutations are thought to be necessary to produce ALL in vivo. This suggests that mutations produced in utero may combine with other mutations, leading to leukemia.32

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