The Japan Society of Human Genetics award lecture. Cytogenetic aspects of cancer-predisposing genes

Cytogenetic responses to G2 phase x-irradiation of cells from retinoblastoma patients

Fibroblast cell lines from 20 retinoblastoma (RB) patients with the hereditary bilateral form of disease compared with 16 lines from normal donors had a significantly higher chromatid aberration frequency (CAF), and more displaced and nondisplaced breaks per 100 metaphase cells after x-irradiation during the G2 phase of the cell cycle. The mean CAF was 39 +/- 1.0, range 30-46, for cells from normal subjects, compared to a mean of 245.6, range 101-506, for cells from hereditary RB patients (p < 10(-6). Of fibroblast lines from eight patients with unilateral RB, four had a CAF comparable to that of lines from normal donors (< 60) and four had a high CAF (> 130), resembling that of hereditary forms; two of the latter four lines were from patients with familial or deletion 13 forms of RB. Furthermore, in two families, PHA-stimulated blood lymphocytes from RB patients, one bilateral and one unilateral, and from certain unaffected first-degree relatives after G2 phase X-irradiation had a high CAF (> or = 110) compared to a CAF (> or = 53) of cells from three normal donors sampled at the same time. These results were shown not to be related to differences in cell cycle progression or initial extent of chromatid damage. The results suggest that the high frequency of chromatid aberrations in the cells from hereditary RB patients results from a genetic deficiency in DNA repair.

The segregation of cancer-causing genes in human populations

Cancer can arise through genetic damage of a variety of sorts, including recessive and dominant mutations, large chromosomal rearrangements, and the inability of cells to repair damaged DNA. Many of these events can be studied by standard methods of genetic analysis and thereby furnish the means to localize the gene to a specific region in the human genome. However, conventional methods of segregation analysis cannot provide the molecular and cellular understanding of the process of gene action essential to informed intervention. Here, recent advances in molecular biology, immunology and biochemistry hold promise of providing the understanding of how normal cells control their replication and why cancer cells do not. Heretofore these techniques have been largely restricted to modest-sized studies, but the requisite assays have now reached a level of development that makes practicable large clinical and population-based studies. Collectively, through these rapidly evolving techniques, we may eventually achieve the acquisition of new methods of prevention, diagnosis and therapy, and a better awareness of the events that order the lives of our cells.

Parental age and seasonal variation in the births of children with sporadic retinoblastoma: a mutation-epidemiologic study

Statistical analysis of parental age data from 225 sporadic cases of bilateral retinoblastoma, plus ten sporadic cases of chromosome deletion or translocation involving 13q14 that was identified as of paternal origin, revealed no evidence of paternal or maternal age effect. Parental exposure to ionizing radiation or chemical mutagens, the effect of which is accumulated with advancing age, does not seem to play a major role in the production of germinal mutations at the responsible (RB) locus. Furthermore, analysis of variation in the month of birth of 753 children with sporadic unilateral retinoblastoma did not show any significant deviation from the controls or a cyclic trend. The occurrence of nonheritable retinoblastoma is not likely to be associated with certain viruses such as human adenovirus 12 whose activity varies markedly with season. These results, together with the fairly uniform pattern in the incidence of this tumor among different populations, suggest that most, if not all, cases of sporadic retinoblastoma are caused by some intrinsic biological mechanisms, and not by environmental mutagens that may vary with respect to time and place.