What is agammaglobulinemia (hypogammaglobulinemia)?

Updated: Jul 08, 2019
  • Author: Donald A Person, MD, FAAP, FACR; Chief Editor: Harumi Jyonouchi, MD  more...
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Answer

Agammaglobulinemia, or hypogammaglobulinemia, is the most common of the primary immunodeficiencies, accounting for approximately 50% of cases. Three major types can be described: X-linked, early onset, and late onset. After more than 50 years since the clinical entity was first described by Bruton in 1952, the molecular defect in X-linked agammaglobulinemia (XLA) has been elucidated. In Bruton's honor, the gene responsible has been named Btk, which stands for Bruton tyrosine kinase. Several historical reviews have been written. [1, 2]

An estimated 90% of patients with early-onset agammaglobulinemia and absence of B cells have abnormalities in the Btk gene (ie, Bruton agammaglobulinemia or XLA). XLA is further discussed in detail in the article Bruton Agammaglobulinemia. Late-onset disease is usually referred to as common variable immunodeficiency (CVID), also described separately. However, reports are increasing of adults who are diagnosed with XLA. An approach in evaluating an adult with hypogammaglobulinemia has been published [3] and possible molecular-genetic mechanisms speculated. [4]

The remaining type is early onset non–Bruton agammaglobulinemia, with low or absent serum immunoglobulin (Ig). Most cases are agammaglobulinemia with autosomal recessive/dominant heritage and represent a very heterogeneous group, including immunoglobulin (Ig) deficiency with increased immunoglobulin M (hyper-IgM syndrome), which is also discussed separately (see X-linked Immunodeficiency With Hyper IgM). In addition, some infants have an initially low Ig level that eventually increases to normal levels. This is known as transient hypogammaglobulinemia of infancy and is discussed in detail in a separate article.

Defective antibody production and low circulating numbers of B cells were described in some female infants and in males in whom no Btk abnormalities were detected. These observations imply the involvement of other genes. This article describes the cases of agammaglobulinemia caused by defects other than Btk. However, because the clinical manifestations and treatments are similar, information from Btk -deficient patients is included because of the lack of sufficient numbers of such patients. Finally, some conditions secondary to acquired immunodeficiency are also described because they need to be recognized in addition to the primary diseases. For other B-cell defects, such as specific Ig deficiencies (eg, immunoglobulin A [IgA] or immunoglobulin G [IgG] subclass deficiencies), refer to the article B-Cell Disorders.


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