The effect of methionine and 5-azacytidine on fragile X expression

The cellular mechanism for the expression of the fragile site at Xq28 is unknown. We tested the effect of 5-azacytidine and methionine on fragile X expression in lymphocytes and lymphoblastoid cells in an attempt to determine if DNA methylation was involved. We were unable to demonstrate a consistent dosage effect of methionine on fragile X expression. While 5-azacytidine was found to inhibit the fragile X in both males and females, it did so only at relatively high concentrations. We conclude that the role, if any, of DNA methylation in fragile X expression is likely to be secondary, the primary effect being due to thymidylate depletion.