Analysis of the B-cell receptor B29 (CD79b) gene in familial chronic lymphocytic leukemia

The B-cell antigen receptor (BCR) comprises membrane Igs (mIgs) and a heter odimer of Ig alpha (CD79a) and Ig beta (CD79b) transmembrane proteins, enco ded by the mb-1 and B29 genes, respectively. These accessory proteins are r equired for surface expression of mig and BCR signaling. B cells from chron ic lymphocytic leukemia (B-CLL) frequently express low to undetectable surf ace Ig, as well as CD79b protein. Recent work described genetic aberrations affecting B29 expression and/or function in B-CLL. Because the prevalence of CLL is increased among first degree relatives, we analyzed the B29 gene in 10 families including 2 affected members each. A few silent or replaceme nt mutations were observed at the genomic level, which never lead to trunca ted CD79b protein. Both members of the same family did not harbor the same mutations. However, a single silent base change in the B29 extracellular do main, corresponding to a polymorphism, was detected on 1 allele of most pat ients. These results indicate that the few mutations observed in the B29 ge ne in these patients do not induce structural abnormalities of the CD79b pr otein and thus do not account for its low surface expression in B-CLL. Furt hermore, genetic factors were not implicated, because identical mutations w ere not observed among 2 members of the same family. (C) 1999 by The Americ an Society of Hematology.