Synergistic effect of hydroxyurea and excessive thymidine on the expression of the common fragile sites at 3p14 and 16q23.

There is a synergistic effect between hydroxyurea (HU) and high concentrations of thymidine (TdR) on the induction of the common fragile sites at 3p14 and 16q23. The frequencies of expression of these fragile sites were significantly higher than in the controls when excessive TdR (0.5 mM) and HU (4 mM) were added into lymphocyte cultures in MEM medium 24 h and 2 h before harvest. Two conditions for the maximum expression of common fragile sites, such as fra(3)(p14), fra(16)(q23) are discussed. The TdR-HU fra(3)(p14)-inducing system might be modified effectively and consistently to improve the prenatal diagnosis of the fragile X syndrome.