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In a series of 126 meningiomas, tumor and patient characteristics were investigated and statistically analyzed. A combined cytogenetic and molecular genetic approach was used to study chromosomal abnormalities and loss of markers on chromosome 22q. This approach was successfully applied to 93 meningiomas. In 66 cases, complete or partial loss of chromosome 22 was observed and in at least 12 of them this chromosome was involved in structural aberrations. In addition to chromosome 22 changes, chromosomes 1, 6, 11, 13, 14, 18, 19, X, and Y were also frequently involved in structural and numerical aberrations. Statistical analysis revealed a significant association between the number of chromosomal abnormalities and tumor grade. Complex karyotypes predominated in the group of grade II/III meningiomas. Furthermore, other variables showed statistically (or marginally statistically) significant differences. Meningiomas from the convexity were more often grade II/III, displayed predominantly (partial) loss of chromosome 22 and had complex karyotypes more often. These features were frequently found in meningiomas from males. Base meningiomas, on the other hand, occurred more often in females; they were usually grade I, showed loss of (parts of) chromosome 22 less often and displayed fewer additional chromosomal abnormalities.

The gene for the hereditary disorder neurofibromatosis type 2 (NF2), which predisposes for benign CNS tumors such as vestibular schwannomas and meningiomas, has been assigned to chromosome 22 and recently has been isolated. Mutations in the NF2 gene were found in both sporadic meningiomas and vestibular schwannomas. However, so far only 6 of the 16 exons of the gene have been analyzed. In order to extend the analysis of an involvement of the NF2 gene in the sporadic counterparts of these NF2-related tumors, we have used reverse transcriptase-PCR amplification followed by SSCP and DNA sequence analysis to screen for mutations in the coding region of the NF2 gene. Analysis of the NF2 gene transcript in 53 unrelated patients with meningiomas and vestibular schwannomas revealed mutations in 32% of the sporadic meningiomas (n = 44), in 50% of the sporadic vestibular schwannomas (n = 4), in 100% of the tumors found in NF2 patients (n = 2), and in one of three tumors from multiple-meningioma patients. Of the 18 tumors in which a mutation in the NF2 gene transcript was observed and the copy number of chromosome 22 could be established, 14 also showed loss of (parts of) chromosome 22. This suggests that in sporadic meningiomas and NF2-associated tumors the NF2 gene functions as a recessive tumor-suppressor gene. The mutations detected resulted mostly in frameshifts, predicting truncations starting within the N-terminal half of the putative protein.

We describe a patient who developed multiple meningiomas but had no clear evidence of neurofibromatosis type 2. Four of the tumors, derived from three different sites, were analyzed cytogenetically and/or at the DNA level using chromosome 22 specific probes. All four tumors showed loss of the same copy of chromosome 22. On the chromosome that was retained in the tumors, we found two constitutional aberrations, a 1.5 kb deletion and a point mutation. The patient had inherited both alterations from her father. The father has not developed any meningiomas so far but he has been treated for a well-differentiated adenocarcinoma of the lung and a brain metastasis from this tumor. The mother and 75 unrelated individuals did not show any of the chromosome 22 alterations. The multiple tumors found in the patient suggest that she has a predisposing gene for the development of meningiomas. The finding that all investigated tumors lost the same, constitutionally normal copy of chromosome 22 could indicate that the predisposing gene resides on chromosome 22 and was affected by the constitutional mutations.

Cytogenetic analysis of meningioma cells from one particular patient (MN32) displayed the stem-line karyo-type 45, XY, -1, 4p+, 22q-, 22q+, which thus had rearrangements of both chromosomes 22. The 22q+ marker appeared as a dicentric: 22 pter----q11::1p11----qter. The reciprocal product of this translocation has presumably been lost because it lacked a centromere. The 22q- chromosome also appeared to have lost sequences distal to band q11. We assumed that this marker could have been the result of a reciprocal translocation between chromosomes 4 and 22. To investigate the 4p+ and 22q- chromosomes in more detail, human-hamster somatic cell hybrids were constructed that segregated the 22q- and 4p+ chromosomes. Southern blot analysis with DNA from these hybrids showed that sequences from 22q were indeed translocated to 4p+ and that reciprocally sequences from 4p were translocated to 22q-, demonstrating a balanced t(4;22)(p16;q11). On the basis of these results we presume that in this tumor a tumor-suppressor gene is deleted in the case of the 22q+ marker and that the t(4;22) disrupts the second allele of this gene. The latter translocation was mapped between D22S1 and D22S15, a distance of 1 cM on the linkage map of this chromosome. The area in which we have located the translocation is within the region where the gene predisposing to neurofibromatosis 2 has been mapped.