 The TEL-AML1 translocation, t(12;21)(p13;q22), is one of the most frequent genetic aberrations in childhood B-cell precursor acute lymphoblastic leukemia (ALL), where it occurs in 25% of all cases.     ///    Evidence suggests that the TEL-AML1 translocation occurs in utero in 1% of all newborn children at cell levels of 10 to 10.     ///    These data indicates that prenatal TEL-AML1 subclones does not persist throughout adult life at cell levels of 10 to 10. 