Changes of common fragile sites on chromosomes according to the menstrual cycle.

The frequencies of chromosomal breaks and sister chromatid exchanges (SCE) are influenced by pregnancy, oral hormonal contraceptives and the menstrual cycle. The changes in the number and sites of spontaneous and aphidicolin-induced breaks on chromosomes from peripheral blood lymphocytes during the menstrual cycle were examined in 8 healthy women. Menstrual cycle was determined by menstruation and the quantity of serum estrogen, progesterone and luteinizing hormone. The number of spontaneous breaks at the follicular phase, the interval phase (which includes ovulation) and the luteal phase were 3.1 +/- 1.1, 2.7 +/- 2.3 and 3.9 +/- 2.6 per 100 mitoses, respectively. The frequencies of aphidicolin-induced breaks in the same phases were 95.8 +/- 23.3, 90.6 +/- 14.3 and 122.7 +/- 20.1 per 100 mitoses, respectively. The higher frequency at the luteal phase was statistically significant compared with the other phases. In the luteal phase, bands 2q32, 3q27, 6q26 and 16q23 had higher frequencies of breaks (P less than 0.05); however, breaks at band 9q32 decreased significantly. SCE showed considerable variation, but with no statistical significance.