Most Common Primary Immunodeficiencies
Selective IgA deficiency is the most common primary immunodeficiency, occurring in 1 in 300-700 live births among white Americans, followed by antibody deficiencies which collectively account for approximately 50% of all primary immunodeficiency disorders. 1
Frequency Hierarchy of Primary Immunodeficiencies
Most Common: Selective IgA Deficiency (SIgAD)
- Incidence: 1 in 300-700 live births in white Americans (though significantly rarer in Asian populations at approximately 1 in 18,000) 1, 2
- Most patients (>50%) remain asymptomatic despite the immunologic defect 2
- Defined as IgA levels <7 mg/dL with normal IgG and IgM levels 2
- Can be drug-induced and potentially reversible with medication cessation 2
Second Most Common Category: Antibody/Humoral Deficiencies
- Account for approximately 50% of all symptomatic primary immunodeficiency disorders 1
- This broad category includes:
- Common Variable Immunodeficiency (CVID): Most common symptomatic antibody deficiency requiring treatment 3, 4
- IgG subclass deficiency 1
- Specific antibody deficiency 1
- Transient hypogammaglobulinemia of infancy 3
- X-linked agammaglobulinemia (Bruton agammaglobulinemia): accounts for 85% of agammaglobulinemia cases 1
Less Common Categories (Each 10-20% of Total)
- Combined B- and T-cell defects: 10-20% of all primary immunodeficiencies 1
- Severe Combined Immunodeficiency (SCID): approximately 1 in 58,000 live births in the United States 1
- Phagocyte defects: 10-20% of all primary immunodeficiencies 1
- Chronic Granulomatous Disease (CGD): 1 in 200,000 live births 1
- Other syndromes: 10-20% of all primary immunodeficiencies, including Wiskott-Aldrich syndrome, DiGeorge syndrome, ataxia-telangiectasia, and hyper-IgE syndromes 1
Rare Categories (Each <1% of Total)
- Diseases of immune dysregulation 1
- Disorders of innate immunity (including NK cell defects) 1
- Autoinflammatory disorders 1
- Complement deficiencies 1
Overall Prevalence Context
- All symptomatic primary immunodeficiencies combined: incidence ranges from 1 in 10,000 to 1 in 2,000 live births 1
- Prevalence in general population: 1 in 10,000 to 1 in 12,000 or more 1
- Male to female ratio is approximately 5:1 in infants and children but approaches 1:1 in adults 1
Critical Clinical Pitfall
Do not dismiss selective IgA deficiency as clinically insignificant simply because most patients are asymptomatic - selected patients suffer from serious complications including recurrent pulmonary infections, autoimmune diseases, gastrointestinal disorders, and malignancy 5. Additionally, some patients with SIgAD can evolve to CVID over time, necessitating long-term monitoring 2.