A new family with fra(10)(q25): spontaneous expression and 100% expression with 100 microM BrdU.

We report on a family with fra(10)(q25) ascertained through a female with multiple minor anomalies and present in her phenotypically normal father and other family members. The site is expressed spontaneously at levels of 9% in lymphocytes, 2% in lymphoblasts, and 6% in skin fibroblasts. Expression frequency is significantly enhanced to levels as high as 100% by addition of BrdU to the culture medium. The consistently high level of induced expression in lymphoblasts from the proband facilitates analysis of the biochemical and structural bases of fragile site expression.