Affecting B cells

X-linked agammaglobulinaemia (Bruton tyrosine kinase deficiency)

Boys with this condition have mutations in the gene for Bruton tyrosine kinase (locus Xq22), resulting in a failure of B-cell development and lack of antibody production. Early infancy is not a problem because of maternally transmitted IgG, but by 2 years of age serious infections become apparent. These include bacterial invasion of the respiratory system, the Gl tract, meninges, joints and skin. Viruses, particularly coxsackie and echoviruses, are also a major threat.

• Absent or very low numbers of B cells.

• Absent or low levels of all immunoglobulins.

• Treatment is by regular antibody replacement with polyvalent IVIg.

Hyper IgM syndrome

An X-linked disorder with B-cell dysfunction due to defective T-cell CD40 ligand production and thus lack of signaling to B-cell CD40 receptors. B cells are normal, but receive no instructions to generate isotypes of Ig other than IgM. Low levels of IgG, IgA and IgE result. There is also deficient function of some tissue macrophages and a tendency to develop Pneumocystis corin/ipneumonia. Treatment is with IVIg replacement therapy and cotrimoxazole prophylaxis.

IgA deficiency

A relatively benign and common disorder affecting 1:500 individuals. They may develop anti-IgA antibodies in serum which can cause urticarial and anaphylactic reactions to blood product infusions. No replacement therapy is needed.

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