Folic acid and chromosome breakage. II. A methionine effect similar to that in fragile X expression.

The absence of folic acid results in an increase in spontaneous chromosome breakage in the presence of, but not in the absence of, methionine. This is similar to the methionine effect seen in studies of the fragile X chromosome. The results support the idea that fragile sites and at least some types of spontaneous chromosome breaks may share a common mechanism.