Kuijpers et al. (2010) reported a Turkish girl, born of consanguineous parents, who developed recurrent respiratory infections and bronchopneumonia at age 2 years. At onset, she had low IgG and low IgA levels. During a follow-up of 4 ... Kuijpers et al. (2010) reported a Turkish girl, born of consanguineous parents, who developed recurrent respiratory infections and bronchopneumonia at age 2 years. At onset, she had low IgG and low IgA levels. During a follow-up of 4 years, she showed normal IgM and IgA levels, but low IgG levels. Laboratory studies showed normal numbers of B cells, but persistent hypogammaglobulinemia, reduced circulating memory B cells, and complete lack of surface CD20 on B cells. There was also a decreased frequency of somatic hypermutations in IgG heavy chain genes and impaired T cell-dependent or -independent IgG antibody formation in vitro. However, patient B cells showed normal proliferation and formation of IgM, indicating intact early development of B cells. In addition, an IgG response could be generated after repeated booster immunization of tetanus toxoid in vivo. B cells of each parent had about 50% CD20 expression compared to controls.