Chromosomal aberrations and bone marrow toxicity.

The importance of chromosomal aberrations as a proximate cause of bone marrow toxicity is discussed. Since chemicals that can cause nondisjunction are rare, numerical aberrations (aneuploidy, polyploidy) are not ordinarily important. Many structural aberrations, however, can lead directly to cell death and so are proximate causes of toxicity when they occur. The micronucleus test which utilizes the polychromatic erythrocyte is capable of detecting agents (clastogens) that can cause such structural aberrations. Many carcinogens can be detected by this test, and recent changes in the protocol may increase the success rate. Nevertheless only a small proportion of chemicals are clastogens. The importance of cell division in the expression of chromosomal damage and the stage of the cell cycle at the time of exposure on the amount of damage is emphasized. A speculative mechanism for the relationship between chromosomal aberrations and carcinogenicity is proposed.