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.

The effect of FUdR on the expression of fra(X)(q27) was examined in lymphocytes and/or fibroblasts from 16 affected males and 5 carriers from 10 families; six different culture media were used: F10, 5% serum, pH 7.3(37 degrees C); medium 199, 5% serum, pH 7.6(37 degrees C); folate-free 199, 5% serum, pH 7.6(37 degrees C), and these three media with FUdR (0.05 micron). 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 four obligate carriers with previously negative results. The fibroblasts from affected males were grown in the six specific media for the last 48 hr. Two of the six 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. It was concluded that FUdR shows promise as an agent to permit prenatal diagnosis of the condition and to enhance the detection of the marker in lymphocyte cultures.