Spontaneous 6-thioguanine-resistant lymphocytes in Fanconi anemia patients and their heterozygous parents.

The incidence of spontaneous 6-thioguanine-resistant (TGr) lymphocytes was studied in the peripheral blood collected from seven Fanconi anemia (FA) patients and five of their heterozygous parents using an autoradiographic or a lymphocyte cloning method. Five of the seven patients showed a significantly elevated incidence of TGr lymphocytes as compared to age- and sex-matched healthy controls. There was, however, no difference between FA heterozygotes and controls. These results suggest some variability among the patients similar to those reported in clinical and cytogenetic investigations. The basis for the increase in TGr cells in the patients is not known, but the inherent genomic instability reflected as increased frequencies of chromosomal aberrations is one possible explanation.