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IgA deficiency
This condition can affect individuals differently, with some experiencing no symptoms and others having a higher risk of recurrent infections, autoimmune diseases, and allergies. It is one of the most common primary immunodeficiencies affecting people of European descent.
Overview
IgA deficiency is a primary immunodeficiency, meaning it is a condition present from birth that affects the immune system. Specifically, it involves a lower than normal amount of immunoglobulin A (IgA) - a type of antibody that plays a crucial role in protecting mucous membranes. These membranes line parts of the body such as the respiratory, gastrointestinal, and genitourinary tracts. IgA acts as a first line of defence against infections in these areas [PMID:33678089]. While some individuals with IgA deficiency experience no health problems, others may be more susceptible to certain infections and other medical conditions. It is considered the most common primary immunodeficiency, particularly among individuals of European ancestry [PMID:28795551].
Symptoms & clinical features
The clinical presentation of IgA deficiency varies widely. Many individuals with low IgA levels do not experience any noticeable symptoms and remain healthy throughout their lives. For those who do have symptoms, recurrent infections are a common feature. These can include ear infections (otitis media), sinusitis, bronchitis, and pneumonia, particularly in the respiratory tract. Gastrointestinal infections and symptoms like diarrhoea may also occur more frequently. In some cases, allergies, such as asthma or allergic rhinitis, appear to be more common in individuals with IgA deficiency. Additionally, there is an increased association with certain autoimmune conditions, where the immune system mistakenly attacks the body's own tissues [PMID:33678089]. These can include coeliac disease, systemic lupus erythematosus, and juvenile idiopathic arthritis, though not everyone with IgA deficiency will develop these.
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Affected organs
IgA is primarily found in mucous secretions, which cover many internal and external surfaces of the body. Therefore, organs and systems with mucous membranes are most commonly affected in IgA deficiency. These include the respiratory tract (nose, sinuses, throat, lungs), the gastrointestinal tract (oesophagus, stomach, intestines), and the genitourinary tract. The eyes and salivary glands also produce IgA, contributing to their protection. While the deficiency itself is systemic, its impact is often localised to these mucosal surfaces, leading to increased vulnerability to pathogens in these areas.
Risks & severity
The severity of IgA deficiency can range from asymptomatic to clinically significant. A significant proportion of individuals with this condition live normal, healthy lives without experiencing any symptoms or complications. However, others may face a lifelong increased risk of recurrent infections, especially of the respiratory and gastrointestinal systems. There is also an elevated risk of developing autoimmune disorders, allergies, and occasionally, lymphoproliferative disorders or certain malignancies. The exact lifetime risk for these associated conditions is difficult to quantify precisely due to the varied nature of the condition. Onset can occur at any age, though it is often diagnosed in childhood or early adulthood when recurrent infections prompt investigation.
Genetic causes
IgA deficiency is understood to have a complex genetic basis, meaning it is influenced by multiple genes and environmental factors, rather than a single gene mutation. Research suggests that variants in several genes may contribute to an individual's susceptibility. One such gene identified is IFIH1 (interferon induced with helicase C domain 1) [PMID:36512399]. The protein produced by IFIH1 plays a role in the immune system's response to viral infections by detecting viral RNA and initiating an antiviral response. While changes in IFIH1 are not the sole cause, certain genetic variants within this gene are thought to modulate immune function and may increase the likelihood of developing IgA deficiency or influence its severity. However, the precise genetic mechanisms are still under active investigation, and other genetic and environmental factors are also believed to play a role.
Inheritance pattern
IgA deficiency generally follows a polygenic or complex inheritance pattern. This means that multiple genes, often working in combination with environmental factors, contribute to an individual's susceptibility to the condition. It does not follow a straightforward dominant or recessive pattern, making it challenging to predict its inheritance within families. While there can be a familial tendency, meaning it may run in some families, not everyone who inherits these genetic predispositions will develop the condition, and individuals with no family history can still be affected. For relatives of someone with IgA deficiency, the risk of also having the condition or being a carrier of predisposing genetic variants can be higher than in the general population, but it is not a guaranteed inheritance.
Diagnosis & testing
Diagnosis of IgA deficiency is typically made by a blood test that measures the levels of immunoglobulins, specifically IgA. A diagnosis is confirmed when serum IgA levels are significantly below the lower limit of normal for age, and other immunoglobulin levels (IgG and IgM) are normal or near normal. This measurement is often repeated to confirm persistent low levels. Referral for testing is usually made by a general practitioner or a specialist, such as an immunologist, particularly if an individual experiences recurrent infections or has a family history of immunodeficiency. In the UK, genetic testing for underlying causes may be considered in some complex cases and would fall under NHS Genomic Medicine Service pathways, potentially utilising relevant R-codes for primary immunodeficiencies if specific genetic causes are suspected.
Management & lifestyle
Management for IgA deficiency is primarily supportive and aims to address symptoms and prevent complications. Since many individuals are asymptomatic, no specific treatment may be necessary. For those who experience recurrent infections, treatment focuses on early and appropriate management of these infections, often involving antibiotics for bacterial infections. Vaccination against common pathogens is generally recommended to reduce infection risk. IgA replacement therapy is generally not effective, as intravenously administered IgA has a very short half-life and does not effectively reach mucosal surfaces. Individuals with associated autoimmune conditions or allergies will receive specific treatment for those conditions. Regular follow-up with a GP or immunologist can help monitor for potential complications and manage symptoms. Lifestyle considerations generally include good hygiene practices and avoiding known triggers for allergies or infections.
UK care pathway
In the UK, individuals suspected of having an immunodeficiency, including IgA deficiency, are typically referred by their GP to an immunology specialist. If a genetic cause is suspected, particularly in complex or syndromic cases, referral to a clinical genetics service may occur. The NHS Genomic Medicine Service provides a pathway for genetic testing for rare diseases, utilising specific R-codes for primary immunodeficiencies. Genetic counsellors play a vital role in explaining inheritance patterns, recurrence risks, and the implications of genetic testing results to patients and their families, ensuring informed decision-making.
Frequently asked questions
What does immunoglobulin A (IgA) do?
Immunoglobulin A (IgA) is an antibody that plays a vital role in protecting the body's mucous membranes. These membranes line the respiratory tract (like the nose and lungs), the gastrointestinal tract (gut), and the genitourinary tract, acting as a first line of defence against germs and infections.
Is IgA deficiency a serious condition?
The seriousness of IgA deficiency varies significantly. Many people with low IgA levels experience no health problems and live normal lives. However, others may have a higher risk of recurrent infections, allergies, or autoimmune conditions. Regular medical follow-up can help monitor for potential issues.
Can IgA deficiency be passed down in families?
IgA deficiency often has a complex inheritance pattern, meaning multiple genes and environmental factors are involved. While it can sometimes run in families, it doesn't follow simple inheritance rules, and not everyone with a genetic predisposition will develop the condition.
How is IgA deficiency treated?
There is no specific cure for IgA deficiency. Treatment focuses on managing symptoms, primarily by treating any recurrent infections with antibiotics. Vaccination is generally recommended. For those without symptoms, no treatment may be necessary. IgA replacement therapy is typically not effective.
What is the prevalence of IgA deficiency in the UK?
IgA deficiency is considered the most common primary immunodeficiency. In populations of European descent, it is estimated to affect approximately 1 in 500 individuals.
References
- Yazdani R, Azizi G, Abolhassani H. Selective IgA Deficiency: Epidemiology, Pathogenesis, Clinical Phenotype, Diagnosis, Prognosis and Management. Scandinavian journal of immunology. 2017. PMID: 27763681
- Schaffer FM, Monteiro RC, Volanakis JE. IgA deficiency. Immunodeficiency reviews. 1991. PMID: 1931006
- Cunningham-Rundles C. Physiology of IgA and IgA deficiency. Journal of clinical immunology. 2001. PMID: 11720003
- Magen E, Merzon E, Green I. Selective IgA deficiency and COVID-19. The journal of allergy and clinical immunology. In practice. 2023. PMID: 36858279
- Quinti I, Mortari EP, Fernandez Salinas A. IgA Antibodies and IgA Deficiency in SARS-CoV-2 Infection. Frontiers in cellular and infection microbiology. 2021. PMID: 33889552
- Zhang J, van Oostrom D, Li J. Innate Mechanisms in Selective IgA Deficiency. Frontiers in immunology. 2021. PMID: 33981304
- Ellis JA. Canine IgA and IgA deficiency: Implications for immunization against respiratory pathogens. The Canadian veterinary journal = La revue veterinaire canadienne. 2019. PMID: 31814637
- Çölkesen F, Kandemir B, Arslan Ş. Relationship between Selective IgA Deficiency and COVID-19 Prognosis. Japanese journal of infectious diseases. 2022. PMID: 34588364