In 1994, the human BMX gene was first identified and cloned in bone marrow cells by Tamagnone et al.[12] The BMX gene is located in chromosomal band X p22.2 between the DXS197 and DXS207 loci.[12] The BTK gene, the closest relative of BMX, is also located in chromosome X. The BMX gene encodes a protein with 675 amino acids, of which 70% are identical with BTK.[12] Mutations in BTK gene are responsible for X-linked agammaglobulinemia (XLA) in humans or X-linked immunodeficiency (XID) in mice.[8] However, diseases-associated BMX gene mutations have not been described yet. Here, BTK is linked to X-linked agammaglobulinemia.