Patient characterization. (A) Serum immunoglobulin titer (IgM and IgG) in P1 show reduced serum IgG and, with IVIG replacement, serum IgM levels dramatically increased. The timing of rituximab and IVIG infusions is shown. (B) Family pedigree. Patients are indicated. (C) Bone marrow aspirate from P1 showing myelokathexis: arrows show degenerative changes and hypersegmentation of mature neutrophils. (D) Schematic representation of signaling pathways activated downstream of the CXCR4 receptor and the effect of the mutations.