Chromosome studies in 70 brain tumors with special attention to sex chromosome loss and single autosomal trisomy.

Chromosome analysis was performed on 70 brain tumors. Thirty-six tumors showed clonal karyotypes characterized by many autosomal abnormalities; 20 meningiomas revealed monosomy 22 as a consistent abnormality, and 12 gliomas showed various abnormalities frequently involving chromosomes 3, 7, and 22. Of the remaining 34 tumors, 24 had normal karyotypes and 10 had clonal cells with loss and/or an extra sex chromosome with single trisomy of chromosomes 3, 6, 7, or 14. Sex chromosome aneuploidy was mostly due to loss of the Y or an X chromosome and was observed in 25 tumors, usually together with autosomal abnormalities. In these tumors the average frequency of cells with sex chromosome aneuploidy was 52%, with a range from 12% to 100%. Loss of the Y was found significantly more frequently in tumors of aged patients. Chromosome analysis in materials subcultured for a long period showed a tendency for cellular selection in which clonal cells with many autosomal abnormalities disappeared rapidly and karyotypes having loss or an extra sex chromosome and/or trisomy 7 were present in an increasing proportion with advance of cell generations in vitro. We infer that the cells having loss of one sex chromosome or trisomy 7 have a proliferative advantage. And that cells bearing only these abnormalities may exist in normal brain tissue more abundantly than in any other body tissue. The possibility of tissue-specific aneuploid mosaicism in the normal tissue would allow an alternative interpretation for simple autosomal trisomy in solid tumors.