TRUNCATING MUTATIONS OF HSNF5 INI1 IN AGGRESSIVE PEDIATRIC CANCER/

Malignant rhabdoid tumours (MRTs) are extremely aggressive cancers of early childhood. They can occur in various locations, mainly the kidne y, brain and soft tissues(1,2). Cytogenetic and molecular analyses hav e shown that the deletion of region 11.2 of the long arm of chromosome 22 (22q11.2) is a recurrent genetic characteristic of MRTs, indicatin g that this locus may encode a tumour suppressor gene(3-8). Here we ma p the most frequently deleted part of chromosome 22q11.2 from a panel of 13 MRT cell lines. We observed six homozygous deletions that deline ate the smallest region of overlap between the cell lines. This region is found in the hSNF5/3INI1 gene, which encodes a member of the chrom atin-remodelling SWI/SNF multiprotein complexes(9-12). We analysed the sequence of hSNF5/INI1 and found frameshift or nonsense mutations of this gene in six other cell lines. These truncating mutations of one a llele were associated with the loss of the other allele. Identical alt erations were observed in corresponding primary tumour DNAs but not in matched constitutional DNAs, indicating that they had been acquired s omatically. The observation of bi-allelic alterations of hSNF5/INI1 in MRTs suggests that loss-of-function mutations of hSNF5/INI1 contribut e to oncogenesis.