Folate metabolism in cells from fragile X syndrome patients and carriers

The in vitro folate sensitivity of the fragile site at Xq27 and the claims of a beneficial response of patients given folic acid prompted us to examine the folate metabolism in cells cultured from fragile X syndrome patients and carriers. Using Epstein-Barr virus we established permanent lymphoblastoid lines from 4 fragile X syndrome males and 3 carriers from 7 families. All these lines expressed the fragile site when 0.1 μM 5-fluorodeoxyuridine (FUdR) was added to the cultures 24 hr prior to harvest; thus, the lines seemed suitable for seeking an intrinsic defect. Fragile X syndrome patient and carrier lines and normal control cell lines did not differ in regard to folate requirements for growth, the ability to use homocysteine in place of methionine, the ability to utilize reduced folates as the sole folate source, or methotrexate sensitivity. These results suggest that no intrinsic defect in folate metabolism is present in fragile X syndrome cells.