Brain tumors are the most frequent childhood tumors. There have been few cytogenetic studies published on these tumors in children compared to the numerous studies on adult brain tumors. We examined chromosomes from 45 primary pediatric brain neoplasms including 14 medulloblastomas, 12 astrocytomas, 4 glioblastomas, 7 ependymomas, 5 craniopharyngiomas, 2 meningiomas, and 1 ganglioglioma. Chromosomal abnormalities were found in 10 medulloblastomas out of the 14 analyzed. The most frequently observed abnormalities were the total or partial loss of one chromosome 17: monosomy 17, i(17q), and a monosomy 22 in 4 cases of desmoplastic medulloblastoma. In glioblastoma, we observed the gain of chromosome 7, chromosome 3, a monosomy 10, and hyperdiploidy. The loss of chromosome X was observed in 2 cases of ependymoma as was a monosomy 22. Our observations show that from the cytogenetic point of view childhood brain tumors differ from adult brain tumors.

Use of specific stains permits analysis of the frequency of nucleolus-associated heterochromatin in chromosomes 1 and 9 from human fibroblasts. In 81 per cent of interphase nuclei the heterochromatic segment of both No. 1 chromosomes is associated with the nucleolus, while in 19 per cent only one heterochromatic segment shows such an association with the other occupying a random position in the nucleoplasm. The nucleolar association of chromosome 9 heterochromatin is less constant: in 42.3 per cent of the nuclei both segments are associated with the nucleolus, in 39 per cent of the nuclei only one heterochromatic segment presents such an association, and in 18.7 per cent neither of the two heterochromatic segments is in nucleolar association. In 6 per cent of the cells, one or two chromosome 9 heterochromatic segments are in contact with the nuclear membrane. In situ hybridization using tritium-labeled 28S and 18S RNA shows that in the interphase nucleus the acrocentric short arms, carriers of ribosomal cistrons, are associated with the nucleolus. These observations demonstrate the complexity of the nucleolus-associated chromatin which, in addition to segments of chromosomes 1, 9, 13, 14, 15, 21, 22, may include the Y chromosome. They also confirm that the nucleolus constitutes one of the orientation points determining the relative localization of chromosomes in the interphase nucleus.

The correlations between cytogenetic and histopathological findings were analyzed in 75 human meningiomas. The tumors were classified according to increasing degrees of anaplasia into three grades: Grade I, benign; Grade II, atypical; Grade III, anaplastic. In 45 tumors of Grade I (benign), we more often observed a normal karyotype or monosomy 22. In 23 tumors of Grade II (atypical), we observed karyotypes with structural and/or numerical abnormalities with the presence of telomeric associations in 8 of them. These last tumors were fibroblastic. In seven Grade III tumors (anaplastic), we also observed complex abnormalities, and in one case, we observed telomeric associations. Our observations show that complex chromosome abnormalities and telomeric associations are observed in tumors that histologically display a certain degree of anaplasia. It is possible that the result of histopathological and cytogenetic correlations might represent a prognostic factor in meningiomas.

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