XDH and glioblastoma: Specifically, cumulative lead exposure as a main effect, estimated on the basis of job history, was not associated with glioblastoma multiforme and meningioma, but polymorphisms in the RAC2 and GPX1 genes (for glioblastoma multiforme) and the GPX1 gene and the XDH gene (for meningioma) were observed to modify the association.