Identification of two complementation groups in Fanconi anemia.

Considerable variation can be observed in the clinical presentation of Fanconi anemia (FA) patients and in the degree of sensitivity of their cells to DNA damaging agents. We have examined the hypothesis that genetic heterogeneity underlies this variation by testing for complementation in somatic cell hybrids constructed from FA cells. Hybrids were formed by fusing lymphoblastoid cell lines derived from four different FA patients. Complementation of the cellular defects in FA was tested by examining sensitivity to growth inhibition by mitomycin C(MMC), spontaneous chromosome breakage, and MMC-induced chromosome breakage in the hybrid cells. These studies revealed the presence of at least two complementation groups, suggesting that there may be two or more different FA genes.