SUMMARY
1. Defects of NF-kB activation lead to ectodermal dysplasia with immunodeficiency. NEMO deficiency causes an X-linked form of disease and a mutation in the IkB protein causes an autosomal dominant form of disease.
2. NF-kB is a central transcription factor that activates the expression of a large number of genes involved in immunity and inflammation. In resting cells NF-kB is inactive and bound to the inhibitor IkB (IkB alpha and IkB beta). Upon cell stimulation, IkB is phosphorylated by an IkB kinase complex that includes NEMO: this allows for dissociation of IkB and translocation of NF-kB to the nucleus to activate gene transcription.
3. Genes upregulated by NF-kB include pro-inflammatory cytokines (TNF-alpha, IL-6, IL-1), chemokines, adhesion molecules, antimicrobial peptides, immunoglobulin class-switching genes, inducible nitric oxide synthetase, and transcription factors that induce type I interferons (IRF3, IRF7). NF-kB is also involved in the differentiation of ectodermal structures.
NEMO deficiency (X-linked Anhidrotic Ectodermal Dysplasia with Immunodeficiency)
-NEMO deficiency is caused by hypomorphic mutations in the NF-kB Essential Modulator (IKBKG gene). NEMO is an essential component of the IkB kinase complex that helps to activate NF-kB. Null mutations (complete loss of function) in the NEMO gene are prenatally lethal in males and causes incontinentia pigmenti in females.
-This disease is characterized by antibody deficiency, low NK cell function, and poor inflammatory cytokine production following TLR stimulation. Some patients have a hyper IgM phenotype (elevated IgA is also commonly seen). Major lymphocyte subset numbers and T cell function (mitogen and antigen induced proliferation) are normal.
-Affected patients suffer from bacterial sinopulmonary infections with encapsulated organisms as well as invasive infections (sepsis, skin abscesses, and meningitis) with S. Pneumoniae, H. Influenzae, Klebsiella, Salmonella, and Pseudomonas.
-Severe Herpes virus infections (HSV, CMV) have been reported. Other viral infections include adenovirus, HPV, and Molluscum contagiosum. Patients can have an increased susceptibility to mycobacterial infections. Pneumocystis jiroveci pneumonia has also been reported.
-Autoimmune abnormalities including hemolytic anemia, arthritis, and inflammatory bowel disease-like colitis have been described.
-In addition to immune defects, ectodermal dysplasia (conical teeth, fine sparse hair, and absence of sweat glands) is found. However, some patients have no evidence of ectodermal dysplasia. Osteopetrosis and lymphedema is a finding in a severe subset of patients.
IKBA Mutation (Autosomal Dominant Anhidrotic Ectodermal Dysplasia with Immunodeficiency)
-Several patients have been reported with a gain of function mutation in IkB (IKBA gene) the inhibitor of NF-kB. This mutation leads to impaired phosphorylation of IkB and prevents its degradation, thus enhancing the inhibitory function of this protein.
-These patients present clinically with failure to thrive, chronic diarrhea, opportunistic infections, and invasive bacterial infections during infancy. Patients also have ectodermal dysplasia and increased susceptibility to atypical mycobacterial infections. The immunologic laboratory profile is similar to patients with NEMO deficiency.
4. Laboratory evaluation of suspected patients should include quantitative immunoglobulins, antibody titers to vaccinations, lymphocyte subset analysis, NK cell functional assay, and toll-like receptor assay.
5. Sequencing of the gene for NEMO (IKBKG) or IkB (IKBA) can confirm the diagnosis.
6. NEMO deficiency and IKBA mutation patients should receive immunoglobulin replacement therapy. Vaccination with BCG vaccine is contraindicated. Prophylactic antibiotics may be indicated in some patients.
7. Survival is variable and depends on the severity of the defects. Some patients die in infancy while other patients survive to adolescence.
8. HSCT is a consideration for patients who have a severe clinical course. However, this therapy will not correct the ectodermal dysplasia seen in patients.
OVERVIEW
NF-B is a central transcription factor that activates the expression of a large number of genes involved in immunity and inflammation. In resting cells NF-kB is inactive and bound to the inhibitor IkB (IkB alpha and IkB beta). Upon cell stimulation, IkB is phosphorylated by the IkB kinase complex that includes NEMO: this allows for the dissociation of IkB and translocation of NF-kB to the nucleus to activate gene transcription.
Genes involved in immunity that are upregulated by NF-kB include pro-inflammatory cytokines (TNF-alpha, IL-6, IL-1), chemokines, adhesion molecules, antimicrobial peptides, immunoglobulin class-switching genes, inducible nitric oxide synthetase, and transcription factors that induce type I interferons (IRF3, IRF7). In addition, genes involved in the proper differentiation of ectodermal structures (skin, hair, teeth) are activated by NF-kB.
Given the central role that NF-kB plays in the activation of the immune response, it is not surprising that defects that impair activation of this transcription factor result in significant combined immune deficiency. NEMO deficiency is an X-linked condition characterized by immunodeficiency and ectodermal dysplasia. IKBA mutations cause an autosomal dominant form of immunodeficiency and ectodermal dysplasia.
NEMO deficiency (X-linked Ectodermal Dysplasia with Immunodeficiency)
-NEMO deficiency is caused by hypomorphic mutations in the NF-kB Essential Modulator (IKBKG gene) located on the X-chromosome. These mutations cause impaired phosphorylation and degradation of the NF-kB inhibitor IkB. As a result, NF-kB is trapped in the cytoplasm and unable to translocate to the nucleus.
-Null mutations (complete loss of function) in the NEMO gene are prenatally lethal in males and cause incontinentia pigmenti in females.
-This disease is characterized by antibody deficiency (hypogammaglobulinemia with poor specific antibody response), low NK cell function, and normal T cell numbers and function (proliferation to mitogens and antigens). Inflammatory cytokine production from toll-like receptor stimulation is decreased. Some patients have elevated IgM and IgA.
-NEMO deficiency patients suffer from bacterial sinopulmonary infections with encapsulated organisms. Invasive infections (sepsis, skin abscesses, and meningitis) with S. Pneumoniae, H. Influenzae, Klebsiella, Salmonella, and Pseudomonas also occur commonly.
-Severe Herpes virus infections (HSV, CMV) have been reported and likely reflect impaired NK cell function. Other viral infections include adenovirus, HPV, and Molluscum contagiosum.
- Patients with mutations in the leucine zipper domain of the NEMO gene have an increased susceptibility to mycobacterial infections due to an impaired IL-12 and IFN- gamma production in response to CD40-CD40L signaling.
-Pneumocystis jiroveci pneumonia has been reported in some patients with NEMO deficiency.
-Autoimmune abnormalities including hemolytic anemia, arthritis, and inflammatory bowel disease-like colitis have been described.
-In addition to immunodeficiency, ectodermal dysplasia (conical teeth, fine sparse hair, and absence of sweat glands) is found in many patients because NF-kB also regulates the development of ectodermal tissues such as skin, hair, and teeth. However, some patients have no evidence of ectodermal dysplasia. Osteopetrosis and lymphedema is a finding that has been reported in 2 patients with a X420W stop codon mutation.
IKBA Mutation (Autosomal Dominant Ectodermal Dysplasia with Immunodeficiency)
-Several patients have been reported with a heterozygous gain of function mutation in IkB (IKBA gene) the inhibitor of NF-kB. This mutation leads to impaired phosphorylation of IkB and prevents its degradation, enhancing the inhibitory function of this protein.
-These patients develop failure to thrive, chronic diarrhea, and opportunistic infections during infancy. Patients also have ectodermal dysplasia and increased susceptibility to atypical mycobacterial infections. However, the father of one affected patient presented with a milder phenotype consisting of recurrent salmonella infections.
-The immunologic laboratory profile is similar to patients with NEMO deficiency.
EVALUATION
Step 1: Quantitative and Functional Humoral Evaluation
-Quantitative immunoglobulins (IgG, IgM, IgA)
-Antibody titers to vaccine antigens
-Lymphocyte flow cytometry for B-cell subpopulations
-Patients can have low IgG but elevated IgM and IgA.
-Protein (Tetanus, Diptheria) and polysaccharide (Pneumococcus) vaccine antibodies should be checked. Specific antibody responses to polysaccharide antigens are often reduced.
-An evaluation of switched memory B cells (CD27+IgM-IgD-) numbers is useful. Impaired CD40-CD40L pathway signaling can lead to impaired B cell class switching.
Step 2: Quantitative and Functional Evaluation of T cells and NK cells
-Flow cytometry for B cell, T cell, and NK cell enumeration
-T cell proliferation to mitogens and specific antigens (candida and tetanus)
-NK cell functional assay
-Lymphocyte subsets (B cell, T cell, NK cell) are usually normal
-T cell proliferation to mitogens and specific antigens is usually normal
-NK cell function is often decreased. In this assay, labeled tumor cells are incubated with NK cells and the lysis of the target cells is measured.
Step 3: Toll-like Receptor Signaling
-Toll-like receptor assay
-Toll-like receptor assays measure inflammatory cytokine production (TNF-alpha, IL-6, and IL-1) following the stimulation of PBMCs with TLR ligands. ---
-Inflammatory cytokine production is decreased in NEMO deficiency and IKBA mutations due to impaired NF-kB activation following TLR signaling.
Step 4: Gene Sequencing
-NEMO Gene Sequencing (IKBKG gene)
-IkB Gene Sequencing (IKBA gene)
-NEMO gene (IKBKG) sequencing is commercially available
-Sequencing for the IkB Gene (IKBA) is also commercially available
MANAGEMENT
As with other antibody deficiency syndromes, replacement of serum IgG with monthly IVIG or weekly subcutaneous immunoglobulin is indicated for patients. Typical IVIG replacement is started with 400-600mg/kg of every 4 weeks or 100-150mg/kg once weekly for subcutaneous immunoglobulin. Trough levels should be maintained above 800mg/dL. The total dose or dosing frequency may be increased to achieve desired troughs and clinical response.
The addition of prophylactic antibiotics can be considered in certain patients who continue to have infections despite appropriate immunoglobulin replacement. Two sample prophylaxis regimens are outlined below:
Amoxicillin 20mg/kg divided twice daily. Maximum of 500mg twice daily.
Azithromycin 10mg/kg once weekly. Maximum of 1 gram once weekly.
Vaccination with Bacille-Calmette-Buerin (BCG) vaccine is contraindicated.
For patients with a severe clinical phenotype and predicted high mortality, HSCT is a consideration. However, the results have been mixed with this therapy and experience is limited.
RESOURCES
Diagnostic Resources
1. Switched Memory B-cells (CD27+IgM-IgD-) by Flow Cytometry
Childrens Hospital of Philadelphia Basic Lymphocyte Panel
Cincinnati Childrens Diagnostic Immunology Laboratory
2. NK cell Functional Assay
Cincinnati Childrens Diagnostic Immunology Laboratory IBT
3. Toll-like receptor assay (ARUP or IBT)
4. Gene Sequencing
Seattle Children's: NEMO Gene Sequencing (IKBKG gene)
Literature Resources
1. Orange 2004
NEMO mutation can result in immunodeficiency without ectodermal dysplasia
2. Orange 2004
Presentation and natural history of immunodeficiency in NEMO mutations
3. Uzel 2005
Range of defects associated with NEMO deficiency
4. Puel 2004
Inherited disorders of NK-kappa B mediated immunity
5. Filipe-Santos 2006
NEMO and Mycobacterial susceptibility due to impaired IL-12 production
6. Courtois 2003
Hypermorphic IkB alpha mutation leads to AD-EDA-ID
7. Janssen 2004
The same IkB alpha mutation leads to two different clinical syndromes
8. McDonald 2007
IkB alpha mutation in a female patient with EDA-ID
9. Orange 2006
TLR functional assay