The molecular genetics of meningiomas.

There are many findings which suggest that an individual may inherit a predisposition for developing a meningioma. The cytogenetics of meningiomas has been well known for some time with monosomy of chromosome 22 as the most characteristic finding. We have confirmed the cytogenetic findings in cultured cells, using molecular genetic techniques on primary tumour tissue. The only difference found between the results of the two techniques was the greater proportion of terminal deletions of the long arm of chromosome 22 detected by the molecular method. The minimal deletion common to 81 meningiomas, and thus the position of the tentative meningioma tumour suppressor gene (TSG), has been determined to lie distal to the myoglobin locus on the long arm of chromosome 22, corresponding to the region 22q12.3-qter. All common histological types of meningioma show the same genetic abnormalities. Study of one tumour with areas of both meningothelial and anaplastic meningioma demonstrated the tumour to be clonal and a partial deletion of 22q to have occurred prior to the development of anaplasia. In order to map in more detail the position of, and finally identify, the TSG involved, a new series of 195 chromosome 22 genomic DNA fragments have been cloned. Current evidence suggests that the genes involved in neurofibromatosis type 2 and meningioma are located at different points on the long arm of chromosome 22 and thus are separate entities.