Different CTNNB1 mutations as molecular genetic proof for the independent origin of four Wilms tumours in a patient with a novel germ line WT1 mutation

We describe a patient with a novel WT1 pS50X germ line mutation, who developed bilateral Wilms tumours, both with stromal-type histology. Both tumours showed loss of the wild type WT1 allele (loss of heterozygosity (LOH)) and a tumour specific mutation in catenin beta1 (CTNNB1), S45P in the left and Δ45S in the right tumour. Molecular analysis of microdissected cells from the left tumour revealed the same S45P CTNNB1 mutation in blastema, tubuli, stroma and muscle, and a different CTNNB1 mutation (T41A) in stromal cells isolated from another area of the same slide. Microdissection of two areas of muscle cells from the right tumour revealed the same Δ45S mutation and no CTNNB1 mutation nor LOH of WT1 in normal kidney cells. One year later, the patient developed a new set of bilateral tumours. Both tumours showed LOH of the wild type WT1 allele, but different CTNNB1 mutations as in the first tumours: S45C on the right and S45F on the left side, demonstrating that these developed independently and are not relapses. This case demonstrates the high risk for the development of Wilms tumours in patients with germ line truncation mutations.