Mutations in the mu heavy-chain gene in patients with agammaglobulinemia.

Most patients with congenital hypogammaglobulinemia and absent B cells are males with X-linked agammaglobulinemia, which is caused by mutations in the gene for Bruton's tyrosine kinase (Btk); however, there are females with a similar disorder who do not have mutations in this gene. We studied two families with autosomal recessive defects in B-cell development and patients with presumed X-linked agammaglobulinemia who did not have mutations in Btk.A series of candidate genes that encode proteins involved in B-cell signal-transduction pathways were analyzed by linkage studies and mutation screening.Four different mutations were identified in the mu heavy-chain gene on chromosome 14. In one fa…