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Primary immunodeficiencies

Posted Oct 13 2009 10:04pm

Antibody

When people talk about immunodeficiency states, they’re usually talking about secondary immunodeficiencies, like AIDS. The primary immune deficiencies really don’t get much press. Which is unfortunate, because although they are much less common than secondary immune deficiencies, they still occur, and it’s important to understand them for that reason alone. Plus, they are very testable – either on board exams, or on class exams.

Time is short, though, and you need to know the basic points for each one without having to wade through a lot of chapters in a textbook. So, without further ado, here is a short, bullet-pointed list of the main disorders, with particular emphasis on the part of the immune system that is affected, and the clinical manifestations of the disease.

X-linked agammaglobulinemia

  • Pre-B cells can’t differentiate into B cells
  • Patients have no immunoglobulin (Ig)
  • X-linked (so seen only in males)
  • Presents at 6 months of age (when maternal Ig runs out)
  • Patients get recurrent bacterial infections
  • Treatment: intravenous pooled human Ig

Common variable immunodeficiency

  • Group of disorders characterized by defective antibody production
  • Affects males and females equally
  • Presents in teens or twenties
  • Basis of Ig deficiency is variable (hence the name) and often unknown
  • Patients more susceptible to infections, but also to autoimmune disorders and lymphoma!

Isolated IgA deficiency

  • Most common of all primary immune deficiencies
  • Cause is unknown
  • Most patients asymptomatic
  • Some patients get recurrent sinus/lung infections or diarrhea (IgA is the major Ig in mucosal secretions)
  • Possible anaphylaxis following blood transfusion (patients have anti-IgA antibodies, and there is IgA in transfused blood!)
  • Increased incidence of autoimmune disease   (who knows why)

Hyper-IgM syndrome

  • Patients make normal (or even increased) amounts of IgM
  • But can’t make IgG, IgA, or IgE!
  • X-linked in most cases
  • Patients also have a defect in cell-mediated immunity
  • Patients have recurrent bacterial infections and infections with intracellular pathogens (e.g., Pneumocystis jiroveci)

DiGeorge syndrome

  • Developmental malformation affecting 3rd and 4th pharyngeal pouches
  • Thymus doesn’t develop well
  • Patients don’t have enough T cells
  • Infections: viral, fungal, intracellular pathogens
  • Patients may also have parathyroid hypoplasia
  • Treatment: thymus transplant!

Severe combined immunodeficiency

  • Group of syndromes with both humoral and cell-mediated immune defects
  • Patients get all kinds of infections
  • Lots of very different genetic defects
  • Half of cases are X-linked
  • Treatment: bone marrow transplantation

The best way to remember these might be to make a little chart, with the diseases in one column, and subsequent columns for transmission (X-linked or not),  immunologic defect (e.g., no immunoglobulin production), and clinical features (e.g., infant with recurrent bacterial infections).

Photo credit: Wikimedia ( http://commons.wikimedia.org/wiki/File:Antibody_je2.png ) via cc license.

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