That chromosome 7 monosomy and 7q22 deletions occur as common secondary events after hyperactivation of Ras oncogenes or mutation of the Ras-GAP protein neurofibromatosis-1 (NF-1) gene may explain the co-occurrence of cavernous malformations with both gliomas and tumors of Schwann cell origin. This evidence concerns the gene NF1 and glioma.