A 13-year-old child presented with three simultaneous malignancies: glioblastoma 
multiforme, Burkitt lymphoma, and colonic adenocarcinoma. She was treated for 
her diseases without success and died 8 months after presentation. Genetic 
analysis revealed a homozygous mutation in the PMS2 gene, consistent with 
constitutional mismatch repair deficiency. Her siblings and parents were 
screened: three of four siblings and both parents were heterozygous for this 
mutation; the fourth sibling did not have the mutation.