Bloom's syndrome in a Japanese boy with lymphoma.

A 14-year-old boy with malignant lymphoma was identified as having Bloom's syndrome after he was shown to display a characteristically elevated frequency of spontaneous sister-chromatid exchanges. Frequencies of sister-chromatid exchanges per nucleus were 80.7 in blood lymphocytes and 29.9 in dermal fibroblasts. Clinical features, although suggestive of Bloom's syndrome, were not clear enough to permit the diagnosis. This is the first confirmed case of this rare genetic disorder in Japan, and in Asia.