Health condition
CTLA-4 haploinsufficiency
CTLA-4 haploinsufficiency is a genetic weakening of one of the immune system's principal brakes, producing a bewildering mix of infections, autoimmunity in multiple organs, gut disease and lymphoid infiltration of the lungs and brain - with targeted treatment (abatacept) available.
Why trust this guide
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Editorial team
Written by our editorial team from the UK sources listed on each page.
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Sourced from guidance
Checked against current NHS and UK specialist society guidance at the time of review.
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Current for 2026
Reviewed on 2026-09-27 with the next review scheduled for 2027-09-27.
Key facts
The essentials at a glance.
The symptoms to recognise, when to seek help, which specialist to see, and what treatment usually involves.
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One faulty CTLA4 gene copy leaves regulatory T cells short of their key brake molecule - immune attack turns inward
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The mixture is the message: hypogammaglobulinaemia with infections PLUS autoimmune cytopenias, enteropathy with diarrhoea, thyroid disease, and lymphocytic infiltration of lungs or brain
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Penetrance is incomplete: a carrier parent may be well while their child is severely affected
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Many patients spend years labelled as 'CVID with complications' before genetics reveals the driver
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Abatacept - a CTLA-4 fusion protein - replaces the missing brake and can transform the disease; sirolimus and immunoglobulin replacement play supporting roles
Understanding the condition
What it is and what happens next.
What causes it, how it is diagnosed, and the treatment routes available in the UK.
What it is and how it feels
CTLA-4 is the checkpoint that oncologists deliberately block to unleash immunity against tumours - and this condition is nature's version of that experiment run lifelong. With only half the normal dose of the brake, regulatory T cells fail at their job, and activated lymphocytes wander into organs they should leave alone: gut lining (chronic diarrhoea and malabsorption), lung (nodules and infiltrates mimicking sarcoidosis or lymphoma), brain, marrow and glands. Antibody production falters simultaneously, so the patient is both infection-prone and autoimmune - a combination that scatters them across specialties.
Diagnosis and treatment routes
Genetic testing pulls the threads together, and matters practically because therapy can address the mechanism: abatacept supplies working CTLA-4 protein and has produced striking responses in infiltrative and gut disease, alongside immunoglobulin replacement for the antibody deficiency and careful use of sirolimus or other agents. Family cascade testing finds carriers who need monitoring rather than mislabelling. Anyone carrying a 'CVID' label plus multi-organ autoimmunity deserves a genetic panel; a private immunology review to organise it is typically available within about two weeks.
Seeing a specialist
Who to see, and how quickly you can be seen.
The specialist for this condition is usually a consultant clinical immunologist. Your GP can refer you on the NHS, or you can arrange a private consultation directly.
A quiet reminder
This guide is for information, not medical advice.
Your GP knows your history and can tell you which parts apply to you. If in doubt, see them - and seek urgent care for any of the emergency symptoms described above.
Frequently asked
Common questions about CTLA-4 haploinsufficiency.
Quick, plain-English answers to what people ask us most.
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What is CTLA-4 haploinsufficiency?
CTLA-4 haploinsufficiency is a genetic weakening of one of the immune system's principal brakes, leading to a mix of increased infections, autoimmunity affecting multiple organs, gut disease, and lymphoid infiltration of organs such as the lungs and brain.
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What causes CTLA-4 haploinsufficiency?
It's caused by an inherited mutation reducing the function of the CTLA-4 gene, which normally helps regulate and restrain immune responses. With only one working copy, the immune system becomes prone to both under- and over-activity.
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What are the symptoms of CTLA-4 haploinsufficiency?
Presentation varies widely but can include recurrent infections, autoimmune conditions (such as low blood counts or thyroid disease), chronic diarrhoea from gut inflammation, and, in some cases, infiltration of organs like the lungs or brain by immune cells.
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Is CTLA-4 haploinsufficiency dangerous?
It can be serious, given the potential for significant autoimmune organ damage and organ infiltration, though severity varies considerably between individuals, even within the same family carrying the same mutation.
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Is CTLA-4 haploinsufficiency hereditary?
Yes, it's inherited in an autosomal dominant pattern, though not everyone who carries the mutation develops significant symptoms (a phenomenon called incomplete penetrance), which is why genetic counselling for affected families is important.
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Can CTLA-4 haploinsufficiency be treated?
Yes - targeted treatment with abatacept, a medication that mimics the CTLA-4 protein's normal regulatory function, can be highly effective at controlling the excessive immune activity seen in this condition.
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How is CTLA-4 haploinsufficiency diagnosed?
Diagnosis typically involves genetic testing once the condition is suspected based on the characteristic combination of infections, autoimmunity, and gut or organ involvement, often after other, more common causes have been considered.
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How long does treatment need to continue?
Treatment with abatacept is generally ongoing long-term, since it addresses the underlying immune dysregulation rather than curing the genetic cause, with regular specialist monitoring to assess response and adjust treatment.
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CTLA-4 haploinsufficiency vs LRBA deficiency - how are they related?
Both conditions affect the same regulatory immune pathway and can cause a similar clinical picture of autoimmunity and immune dysregulation, but they're caused by mutations in different genes, and genetic testing is needed to distinguish them precisely.
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When should I see a specialist about possible CTLA-4 haploinsufficiency?
See an immunology specialist if you or a family member has a combination of recurrent infections, unexplained autoimmune disease, and gut symptoms. Given the rarity, referral to a specialist immunodeficiency centre is recommended, ideally without delay.