Tumor cells from 70% of neuroblastoma patients contain a deletion of part of the short arm of chromosome 1, indicating that this chromosomal region includes a gene involved in tumor formation. To more precisely evaluate the boundaries and mechanisms involved in generating these deletions, we have examined four neuroblastoma cell lines using a combination of somatic cell hybridization, isozyme analysis, and nucleic acid hybridization employing both standard and restriction fragment length polymorphic probes. The data suggest that the truncation of chromosome 1 in these neuroblastomas was most likely due to a complex translocation and deletion mechanism rather than a simple unbalanced translocation or terminal or interstitial deletion. This conclusion is supported by the frequent removal of MYCL from the altered chromosome 1 to another chromosome. Furthermore, the data suggest that the frequency of breakpoints previously assigned by karyotypic analysis to bands other than lp32 in neuroblastomas may be overestimated. Finally, this study identified a breakpoint at 1p32 that was localized between the genes JUN and MYCL for one neuroblastoma thus establishing the order of these genes as centromere, JUN, MYCL, telomere. We conclude that the observed breakpoints within chromosome 1p in human neuroblastoma are not as variable as previously described and suggest the results of this study provide evidence for the involvement of specific DNA sequences within lp32 in the generation of neuroblastoma.

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