Chromosome region 11p15.5 harbors unidentified genes involved in neoplasms and in the genetic disease Beckwith-Wiedemann syndrome. The genetic analysis of a 170-kb region at 11p15.5 between loci D11S601 and D11S679 resulted in the identification of six transcriptional units. Three genes, hNAP2, CDKN1C, and KVLQT1, are well characterized, whereas three genes are novel. The three additional genes were designated BWR1A, BWR1B, and BWR1C. Full-length cDNAs for these three genes were cloned and nucleotide sequences were determined. While our work was in progress, BWR1C cDNA was described as IPL [Qian, N., Franck, D., O'Keefe, D., Dao, D. , Zhao, L., Yuan, L., Wang, Q., Keating, M., Walsh, C. & Tycko, B. (1997) Hum. Mol. Genet. 6, 2021-2029]. The cloning and mapping of these genes together with the fine mapping of the three known genes indicates that the transcriptional map of this region is likely to be complete. Because this region frequently is altered in neoplasms and in the genetic disease Beckwith-Wiedemann syndrome, we carried out a mutational analysis in tumor cell lines and Beckwith-Wiedemann syndrome samples that resulted in the identification of genetic alterations in the BWR1A gene: an insertion that introduced a stop codon in the breast cancer cell line BT549 and a point mutation in the rhabdomyosarcoma cell line TE125-T. These results indicate that BWR1A may play a role in tumorigenesis.