Mapping of chromosome 20 for loss of heterozygosity in childhood ALL reveals a 1000-kb deletion in one patient

The long arm of chromosome 20 displays recurrent loss of heterozygosity (LO H) for microsatellite markers in blast cells from children with acute lymph oblastic leukemia. To further characterize the region of deletion and to pr ecisely establish its frequency, we searched for LOH in 103 children with A LL using polymorphic markers in the previously described region of interest , namely between D20S101 and D20S887, LOH was detected in nine patients (ie with a frequency of 8.7%). Interestingly, in one patient, a small deletion was found, flanked proximally by D20S850 and distally by M201, a dinucleot ide repeat identified from chromosome 20 sequences. The distance between th ese two markers is approximately 1000 kb, The occurrence of non-random dele tions of the long arm of chromosome 20 has previously been observed in myel oid malignancies (myeloproliferative disorders and myelodysplastic syndrome s) in 5-10% of patients. The small deletion in our patient is located withi n the common region of deletion of myeloproliferative disorders suggesting that a tumor suppressor gene may be the common target of the deletions in v arious types of hematological malignancies.