Correlation of germ-line mutations and two-hit inactivation of the WT1 gene with Wilms tumors of stromal-predominant histology (histopathologyytruncation mutationsytumor suppressor geneynephroblastomaySSCP analysis)

The WT1 gene, located on chromosome 11p13, is mutated in a low number of Wilms tumors (WTs). Germ-line mutations in the WT1gene are found in patients with bilateral WT andyor associated genital tract malforma- tions (GU). We have identified 19 hemizygous WT1 gene mutationsydeletions in 64 patient samples. The histology of the tumors with mutations was stromal-predominant in 13, triphasic in 3, blastemal-predominant in 1, and unknown in 2 cases. Thirteen of 21 patients with stromal-predominant tumorshadWT1mutationsand10ofthesewerepresentinthe germ line. Of the patients with germ-line alterations, six had GU and a unilateral tumor, two had a bilateral tumor and normalGUtracts,andtwohadaunilateraltumorandnormal GU. Three mutations were tumor-specific and were found in patients with unilateral tumors without GU. These data demonstrate a correlation of WT1mutations with stromal- predominant histology, suggesting that a germ-line mutation in WT1predisposes to the development of tumors with this histology.Twelvemutationsarenonsensemutationsresulting in truncations at different positions in the WT1 protein and only two are missense mutations. Of the stromal-predomi- nant tumors, 67% showed loss of heterozygosity, and in one tumor a different somatic mutation in addition to the germ- line mutation was identified. These data show that in a large proportionofahistopathologicallydistinctsubsetofWTsthe classical two-hit inactivation model, with loss of a functional WT1 protein, is the underlying cause of tumor development.