biology

Selective immunoglobulin A deficiency

Selective immunoglobulin A deficiency is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Selective immunoglobulin A deficiency rather than just read about it. In short: Selective immunoglobulin A (IgA) deficiency (SIgAD) is a kind of immunodeficiency, a type of hypogammaglobulinemia. People with this deficiency lack immunoglobulin A (IgA), a type of antibody that protects against infections of the mucous membranes lining the mouth, airways, and digestive tract.

Key takeaways

Selective immunoglobulin A deficiency belongs to biology; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Selective immunoglobulin A deficiency to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Selective immunoglobulin A deficiency from memory before moving on to harder problems.

Reference excerpt

Selective immunoglobulin A (IgA) deficiency (SIgAD) is a kind of immunodeficiency, a type of hypogammaglobulinemia. People with this deficiency lack immunoglobulin A (IgA), a type of antibody that protects against infections of the mucous membranes lining the mouth, airways, and digestive tract. It is defined as an undetectable serum IgA level in the presence of normal serum levels of IgG and IgM, in people older than 4 years. It is the most common of the primary antibody deficiencies. However, most people with the condition remain healthy throughout their lives and are never diagnosed.

Signs and symptoms 85–90% of IgA-deficient individuals are asymptomatic, although the reason for lack of symptoms is relatively unknown and continues to be a topic of interest and controversy. Some patients with IgA deficiency have a tendency to develop recurrent sinopulmonary infections, gastrointestinal infections and disorders, allergies, autoimmune conditions, and malignancies. These infections are generally mild and would not usually lead to an in-depth workup except when unusually frequent. They rarely present with severe reactions, including anaphylaxis, to blood transfusions or intravenous immunoglobulin due to the presence of IgA in these blood products. Patients have an increased susceptibility to pneumonia and recurrent episodes of other respiratory infections and a higher risk of developing autoimmune diseases in middle age. IgA deficiency and common variable immunodeficiency (CVID) feature similar B cell differentiation arrests, but it does not present the same lymphocyte subpopulation abnormalities. IgA-deficient patients may progress to panhypogammaglobulinemia characteristic of CVID. Selective IgA and CVID are found in the same family. Recent research suggests that while selective IgA deficiency may not increase susceptibility to initial SARS-CoV-2 (COVID 19) infection, it may be associated with a higher risk of recurrent infection and hospitalisation.

Cause Selective IgA deficiency is inherited in less than half of cases, but has been associated with differences in chromosomes 18, 14 and 6. Selective IgA deficiency can be inherited, but fewer than half of all cases have been associated with some congenital intrauterine infections.

Pathophysiology Pathogenesis of IgA Deficiency 'In IgA-deficient patients, the common finding is a maturation defect in B cells to produce IgA'. 'In IgA deficiency, B cells express IgA; however, they are of immature phenotype with the coexpression of IgM and IgD, and they cannot fully develop into IgA-secreting plasma cells'. There is an inherited inability to produce immunoglobulin A (IgA), a part of the body's defenses against infection at the body's surfaces (mainly the surfaces of the respiratory and digestive systems). As a result, bacteria at these locations are somewhat more able to cause disease. Types include:

Diagnosis When suspected, the diagnosis can be confirmed by laboratory measurement of IgA level in the blood. SIgAD is an IgA level < 7 mg/dL with normal IgG and IgM levels (reference range 70–400 mg/dL for adults; children somewhat less).

Treatment The treatment consists of identification of co-morbid conditions, preventive measures to reduce the risk of infection, and prompt and effective treatment of infections. Infections in an IgA-deficient person are treated as usual (i.e., with antibiotics). There is no treatment for the underlying disorder. All SIgAD patients, even if asymptomatic, should receive pneumococcal and influenza vaccines, but should avoid live attenuated vaccines.

Use of IVIG as treatment There is a historical popularity in using intravenous immunoglobulin (IVIG) to treat SIgAD, but the consensus is that there is no evidence that IVIG treats this condition. In cases where a patient presents SIgAD and another condition which is treatable with IVIG, then a physician may treat the other condition with IVIG. The use of IVIG to treat SIgAD without first demonstrating an impairment of specific antibody formation is not recommended.

Prognosis Prognosis is excellent, although there is an association with autoimmune disease. Of note, selective IgA deficiency can complicate the diagnosis of one such condition, celiac disease, as the deficiency masks the high levels of certain IgA antibodies usually seen in celiac disease. As opposed to the related condition CVID, selective IgA deficiency is not associated with an increased risk of cancer. Patients with Selective IgA deficiency rarely have severe reactions to blood transfusions. Although Selective IgA deficiency is common, severe reactions to blood transfusions are very rare. People with selective IgA deficiency do not require special blood products unless they have a history of a severe allergic reaction to a blood transfusion. Patient education and ongoing monitoring are important components of care, particularly to identify complications such as recurrent infections or autoimmune disease.

Epidemiology Prevalence varies by population, but is on the order of 1 in 100 to 1 in 1000 people, making it relatively common. SIgAD occurs in 1 in 39 to 1 in 57 people with celiac disease. This is much higher than the prevalence of selective IgA deficiency in the general population. It is also significantly more common in those with type 1 diabetes. It is more common in males than in females.

Illustrations

Worked examples

Example 1 — a first encounter with Selective immunoglobulin A deficiency

Start with the simplest possible case. Write down what Selective immunoglobulin A deficiency claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Selective immunoglobulin A deficiency before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Selective immunoglobulin A deficiency ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Selective immunoglobulin A deficiency

In research: Selective immunoglobulin A deficiency appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Selective immunoglobulin A deficiency in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Selective immunoglobulin A deficiency is common in secondary-school and first-year university syllabi. It links to neighbouring topics Immune system disorders, Noninfectious immunodeficiency-related cutaneous conditions, Predominantly antibody deficiencies, so understanding it makes those chapters shorter.
In everyday life: Look for Selective immunoglobulin A deficiency outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Selective immunoglobulin A deficiency in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Selective immunoglobulin A deficiency means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Selective immunoglobulin A deficiency out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Selective immunoglobulin A deficiency in simple terms?

Why does Selective immunoglobulin A deficiency matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Selective immunoglobulin A deficiency?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Selective immunoglobulin A deficiency.