Liability to Chromosome Damage in Lymphocytes of “Cancer Family” Subjects: A Study of Spontaneous and Induced Chromosomal Fragility

Spontaneous chromosomal fragility was detected in seven tumor patients and one healthy member from two families with a high recurrence of cancer. Major chromosome lesions, such as terminal deletions and rearranged chromosomes, were found at levels significantly higher than those reported for control individuals. The prevalence of these aberrations in comparison to minor ones (chromosome gaps and chromatid breaks) in this group ofpatients seems to indicate that the fragility observed is the end-point of a process of chromosomal instability, which may have already been brought to expression. Study of other parameters of genetic instability in the most unstable karyotypes showed that the chromosome damage observed was neither paralleled by abnormal SCE frequency nor sustained by defective DNA repair mechanisms or expression of inherited or constitutional fragile sites. As all the subjects investigated here had previously been shown to display intraindividual variations in the C-banded region of chromosome 1, it is possible that spontaneous fragility and acquired C-heterochromatin polymorphism may be markers that, combined with chromosomal instability, create genetic predisposition to cancer.

19p deletion in recurring leiomyosarcoma lesions from the same patient

Ten leiomyosarcomas (LMS) affecting the same patient over a period of 3 years were cytogenetically studied to detect nonrandom chromosomal changes with a pathogenetic significance. All tumors, likely metastases of a previous LMS presentation, were classified as small, including eight that developed before chemotherapy; the diagnoses were based on standard immunohistochemistry methods for smooth muscle tumors. Scoring of 613 metaphases revealed monosomy of chromosome 22 in six LMS, monosomy of chromosome 19 in three, and deletion of chromosome 19p in all ten. Interphase fluorescence in situ hybridization (FISH) of the 22-alphoid-specific probe allowed loss of the target chromosome to be detected in four tumors at higher frequencies than those detected by cytogenetics. Double-color FISH of the 19p- and 19q-specific YAC performed on one tumor made it possible to distinguish the monosomic and 19p deleted cells, the relative frequencies of which were found to be 10% and 20%, respectively. The deletion breakpoint could be mapped at 19p13 between YAC 957d12 and YAC 947g4. The recurrence of the 19p deletion in a subset of tumor cells from all of the analyzed LMS suggests that this structural aberration is a significant change in the development of leiomyosarcomas.

Mosaicism in the C-banded region of chromosome 1 in cancer families

Chromosome 1 C-band length mosaicism was detected in lymphocytes from six tumor patients and one healthy subject belonging to three families with a high incidence of cancer. In all cases the variant cell population showed a decreased amount of C-heterochromatin in one chromosome, whereas the C-banded pattern of the homolog was identical to that of the nonvariant cell population. A family tendency to unequal mitotic crossing over, possibly leading to C-band heteromorphism, may explain the high frequency of detection of C-heterochromatin mosaicism in cancer family members (seven of 13 cases studied). The possible role of heterochromatin in inducing cancer has been widely discussed. The special feature of the acquired C-band variants vis-à-vis the inherited ones is that they mark intrinsic genetic instability that may result, through multiple mechanisms, in increased susceptibility to malignancy.

Cytogenetic analysis and muscle differentiation in a girl with severe muscular dystrophy

The uncommon case is described of a girl severely affected with Duchenne muscular dystrophy. Cytogenetic analysis revealed no numerical or structural abnormalities of the X-chromosome in any of the cells examined (leucocytes and myoblasts). No abnormality in morphology, growth pattern or differentiation was observed in the dystrophic muscle cultures as compared with control cultures.