The fragile X(q27) form of X-linked mental retardation: FUdR as an inducing agent for fra(X)(q27) expression in lymphocytes, fibroblasts, and amniocytes

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Abstract
The effect of FUdR [5-fluorodeoxyuridine] on the expression of fra(X)(q27) was examined in lymphocytes and/or fibroblasts from 16 affected males and 5 carriers from 10 families; 6 different culture media were used: F10, 5% serum, pH 7.3 (37.degree. C); medium 199, 5% serum, pH 7.6 (37.degree. C); folate-free 199, 5% serum, pH 7.6 (37.degree. C), and these 3 media with FUdR (0.05 .mu.m). In lymphocytes there was no significant difference in the percentage of fra(X) expressing cells between any of the FUdR-containing media. The highest percentage of expressing cells seen in lymphocytes with FUdR was 56%. The average enhancement in males with FUdR in the 199 and folate-free 199 media was 30%. This relative enhancement with FUdR was very much higher in a few blood specimens delayed in transit and FUdR may prevent some of the false-negative results obtained from mailed specimens. FUdR did not induce the marker in 4 obligate carriers with previously negative results. The fibroblasts from affected males were grown in the 6 specific media for the last 48 h. Two of the 6 media yielded reproducibly positive results. These were 199-FUdR and folate-free 199-FUdR with mean percentages of expressing cells of 12.8 .+-. 7.1% and 11.3 .+-. 6.1%, respectively. F10-FUdR, which contains thymidine, did not permit expression of the marker in fibroblasts and there was no difference in the percentage of fra(X) expression in 199-FUdR media with or without folate. FUdR shows promise as an agent to permit prenatal diagnosis of the condition and to enhance the detection of the marker in lymphocyte cultures.