Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) X-linked agammaglobulinemia ?
    ### Response:
    X-linked agammaglobulinema is a primary immunodeficiency characterized by very low levels of immunoglobulins (proteins made by the immune system to help fight infections). People affected by this condition generally begin developing frequent and recurrent bacterial infections from about 6 months of age.
    