Loss of X chromosome in childhood acute lymphoblastic leukemia.

We present six cases of childhood acute lymphoblastic leukemia (ALL) in which an acquired loss of the X chromosome was detected. The cases derive from a consecutive series of 178 childhood ALL, consisting of 80 girls and 98 boys. In five cases the presence of the TEL-AML1, t(12;21), fusion product was detected by FISH. The single negative case had an unusual t(1;19)(p13;q13). In addition, this was the only case that did not have a cytogenetically visible rearrangement involving one of the chromosome regions 6q, 9p, or 12p. The six cases showed the typical presentation features of an ALL of FAB type L1, a common ALL immunophenotype with myeloid marker co-expression, and a median presenting age of 7 years. We, therefore, conclude that loss of chromosome X may be a secondary event in older girls with TEL-AML1-positive ALL.