This gene encodes a cytoplasmic linker or adaptor protein that plays a critical role in B cell development.This protein bridges B cell receptor-associated kinase activation with downstream signaling pathways, thereby affecting various biological functions.The phosphorylation of five tyrosine residues is necessary for this protein to nucleate distinct signaling effectors following B cell receptor activation.Mutations in this gene cause hypoglobulinemia and absent B cells, a disease in which the pro- to pre-B-cell transition is developmentally blocked.Deficiency in this protein has also been shown in some cases of pre-B acute lymphoblastic leukemia.Alternatively spliced transcript variants encoding different isoforms have been found for this gene.[provided by RefSeq]