FREQUENT HOMOZYGOUS DELETIONS OF D13S218 ON 13Q14 IN B-CELL CHRONIC LYMPHOCYTIC-LEUKEMIA INDEPENDENT OF DISEASE STAGE AND RETINOBLASTOMA GENE INACTIVATION

A correlative study has been performed to delineate further the role o f the Rb gene in the disease B-cell chronic lymphocytic leukemia (B-CL L), First, we examined DNAs from B cells from 140 B-CLL patients repre senting all Rai stages of disease for the loss of 13q14 using two micr osatellite markers mapping distal to the Rb locus, Loss of heterozygos ity (LOH) of D13S133 was infrequent, occurring in 5 of 140 (4%) patien ts, The frequency for LOH of D13S218 was 33 of 140 (24%) samples and w as independent of Rai stage of disease, Rb protein was detected in 19 of 23 (83%) samples. Of 4 patients lacking detectable Rb gene expressi on, only one showed LOH of D13S218. Rb protein levels varied from unde tectable to high in samples with or without LOH for D13S218, and the l evels were also independent of Rai stage of disease, Our findings supp ort the role of DBM on 13q14, rather than Rb, as the candidate tumor s uppressor gene that is frequently targeted for deletion in B-CLL. In a ddition, the data suggest that other mechanism(s) contribute to altere d Rb expression detected in one-fourth of B-CLL B-cells.