Mutations in the Mu Heavy-Chain Gene in Patients with Agammaglobulinemia

TLDR: Defects in the mu heavy-chain gene are a cause of agammaglobulinemia in humans, which implies that an intact membrane-bound mu chain is essential for B-cell development.

Abstract: Background 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. Methods A series of candidate genes that encode proteins involved in B-cell signal-transduction pathways were analyzed by linkage studies and mutation screening. Results Four different mutations were identified in the mu heavy-chain gene on chromosome 14. In one family, there was a homozygous 75-to-100-kb deletion that included D-region genes, J-region genes, and the mu constant-region gene. In a second family, there was a homozygous base-pair substitution in the alternative splice site of the mu heavy-chain gene. This mutation would inhibit productio...