Increased expression of fragile site Xq by hydroxyurea. Preliminary communication.

The addition of hydroxyurea in final concentration 1.3 X 10(-5) M increases the frequency of fraX in comparison with cultures without hydroxyurea. The same concentration of hydroxyurea did not induce fraX formation and "nonspecific" gaps in cultures of lymphocytes derive from healthy individuals. The possible explanation of this effect is discussed.