Patients are prone to bacterial infections.
The disease is manifested as a B cell differentiation defect. As the differentiation block results in severely decreased numbers of B lymphocytes and an almost complete lack of plasma cells, the immunoglobulin levels are very low. Prior to gammaglobulin substitution therapy and treatment with antibiotics the disease was invariably lethal at a young age. The Btk gene is located in the X chromosome, in the Xq22 region. As in most other genes, mutations are mainly found in exons and splice sites.