Humoral (antibody) immunodeficiency syndromes

What it is

The humoral immunodeficiency syndromes are the B-cell disorders, and they are separated by two things: the B cell count, and which immunoglobulins are low.

• CD40 ligand deficiency (hyper-IgM syndrome): B cell count normal; IgG low, IgA low, IgM high, IgE low.
• Common variable immunodeficiency: B cell count normal; IgG, IgA, IgM and IgE all low.
• Job syndrome (hyper-IgE syndrome): B cell count normal; IgG, IgA and IgM normal; IgE high.
• Selective IgA deficiency: B cell count normal; IgA low, the rest normal.
• X-linked agammaglobulinemia: B cell count low; IgG, IgA, IgM and IgE all low.

The main difference between CVID and Bruton is therefore the B cell count, since both of them lower all the immunoglobulins.

Causes and risk

X-linked (Bruton) agammaglobulinemia is a defect in BTK, a tyrosine kinase gene, so there is no B-cell maturation. It is X-linked recessive, and so is commoner in boys.

Selective IgA deficiency has an unknown cause and is the most common 1° immunodeficiency.

Common variable immunodeficiency is a defect in B-cell differentiation whose cause is unknown in most cases.