77Confounding, Reverse Causation, and Ecological Fallacy
around the age of 2–5 years, whereas the incidence of AML increases with increasing age.
Such differences make a single causal exposure or mechanism unlikely [47].
Both subtypes are thought to develop through a rst initiating genetic event in utero
followed by further postnatal genetic changes [48–50]. The most common chromosomal
abnormalities observed in ALL are hyperdiploidy (35% of cases) and the TEL-AML1 gene
fusion (25%). Chromosomal translocations occur in utero; the prevalence of TEL-AML1
fusion gene in newborns has been estimated at around 1%, but only 1% of these children
will develop ALL with a TEL-AML1 gene fusion before the age of 15 years [48]. Thus, a
“second hit” is a critical ...