Congenital Immunodeficiency Disorders

Congenital immunodeficiency disorders are genetically determined conditions characterized by deficiencies, absences, or defects in one or more components of the immune system. These disorders often manifest in infancy or childhood with recurrent, chronic, or opportunistic infections, and their diagnosis relies on immunological and genetic testing. Treatment primarily focuses on preventing and managing infections, with the prognosis varying depending on the specific disorder.

Congenital B-cell immunodeficiencies involve defects in B-cell development or function, leading to reduced antibody production. X-linked (Bruton) agammaglobulinemia results from a BTK gene defect, causing a complete deficiency of mature B cells and recurrent pyogenic infections, especially by encapsulated bacteria, typically presenting between 3 and 6 months of age. Selective IgA deficiency, the most common primary immunodeficiency, often remains asymptomatic but can manifest with respiratory infections or chronic diarrhea, and is associated with autoimmune diseases. Common variable immunodeficiency (CVID) is characterized by phenotypically normal B cells that cannot differentiate into plasma cells, leading to low immunoglobulin levels and recurrent sinopulmonary infections, typically developing between 20-40 years of age.

Congenital T-cell immunodeficiencies affect T-cell development or function. DiGeorge syndrome, caused by a microdeletion at 22q11.2, results in defective development of the third and fourth pharyngeal pouches, leading to hypoplastic thymus and parathyroids, with variable phenotypes including cardiac anomalies, facial abnormalities, thymus aplasia/hypoplasia, cleft palate, and hypocalcemia. Autosomal dominant hyper-IgE syndrome (Job syndrome), caused by a STAT3 gene mutation, results in decreased Th17 cells and defective neutrophil chemotaxis, characterized by coarse facial features, recurrent abscesses, retained primary teeth, hyper-IgE, eosinophilia, and severe eczema. IL-12 receptor deficiency, inherited in an autosomal recessive pattern, impairs the Th1 response, predisposing individuals to disseminated mycobacterial and fungal infections. IPEX syndrome, an X-linked recessive disorder, involves a FOXP3 gene mutation, leading to impaired regulatory T cells and autoimmunity, typically presenting in early infancy with lymphadenopathy, autoimmune skin and endocrine disorders, enteropathy, and failure to thrive.

Congenital combined immunodeficiencies involve defects affecting both B and T cells. Severe combined immunodeficiency (SCID) results from various mutations, including X-linked recessive defects in the IL-2R gamma chain and autosomal recessive defects in adenosine deaminase, leading to impaired B and T cell function and recurrent infections, chronic diarrhea, and failure to thrive. Wiskott-Aldrich syndrome (WAS), an X-linked recessive disorder, is caused by a WAS gene mutation, leading to impaired remodeling of the T-cell actin cytoskeleton and defective antigen presentation, characterized by purpura, eczema, and recurrent pyogenic infections. Hyper-IgM syndrome involves a class-switching defect of Th cells, most commonly CD40 ligand deficiency, leading to recurrent sinopulmonary and opportunistic infections. Ataxia telangiectasia, an autosomal recessive disorder, results from an ATM gene defect, leading to failure to repair dsDNA breaks and increased susceptibility to infections and malignancy, presenting with progressive ataxia, spider angiomas, and IgA deficiency.

Congenital neutrophil and phagocyte disorders affect the function of neutrophils and phagocytes. Chronic granulomatous disease (CGD) is caused by a defective phagocytic NADPH oxidase, leading to decreased ROS production and recurrent infections with catalase-positive organisms. Leukocyte adhesion deficiency type 1 (LAD1) results from an absent LFA-1 protein, impairing leukocyte chemotaxis and migration, leading to recurrent nonsuppurative bacterial infections and impaired wound healing. Chédiak-Higashi syndrome involves a LYST gene defect, leading to defective neutrophil chemotaxis and phagosome-lysosome fusion, characterized by partial albinism, lymphohistiocytosis, peripheral neuropathy, and recurrent pyogenic infections. Myeloperoxidase deficiency, an autosomal recessive disorder, involves a mutation in the MPO gene, leading to partial or complete deficiency of MPO in phagocytes and recurrent Candida infections.

Congenital complement deficiencies involve defects in complement components, leading to impaired opsonization and immune complex clearance. C1 esterase inhibitor deficiency results in unregulated activation of kallikrein and increased bradykinin, leading to recurrent angioedema. Early complement deficiencies, such as C1, C2, and C4 deficiencies, increase the risk of recurrent infections and autoimmune diseases like SLE. C3 deficiency impairs opsonization and increases susceptibility to encapsulated bacteria and type III hypersensitivity reactions. Terminal complement deficiencies, such as C5, C6, and C8 deficiencies, impair the formation of the membrane attack complex, leading to recurrent Neisseria infections and an increased risk of SLE and glomerulonephritis.

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