A hereditary angioedema genetic test looks for inherited variants that can cause repeated swelling through excessive bradykinin activity. The most common form involves SERPING1, the gene for C1 inhibitor. Other forms can involve F12, PLG, ANGPT1, KNG1, MYOF, HS3ST6, and additional genes linked to hereditary angioedema with normal C1 inhibitor. Genetic testing can confirm a suspected diagnosis, identify relatives at risk, and distinguish some inherited cases from acquired angioedema, but it does not replace complement testing or clinical evaluation. A negative panel does not rule out hereditary angioedema, especially when C1 inhibitor levels and function are normal, because not every causative gene is known. Swelling of the tongue, throat, or airway is a medical emergency. Hives and itching usually point toward histamine-mediated allergy rather than classic hereditary angioedema, although real patients can have more than one condition. Results should be reviewed by an allergy or immunology specialist familiar with bradykinin-mediated swelling.
- SERPING1 variants cause most hereditary angioedema with low or dysfunctional C1 inhibitor.
- F12 and PLG are established causes of some hereditary angioedema with normal C1 inhibitor.
- A pathogenic variant can confirm inherited risk, but symptom severity cannot be predicted precisely.
- A negative genetic result does not exclude hereditary angioedema when the clinical pattern is convincing.
- Throat, tongue, or breathing symptoms require emergency treatment immediately.
Table of Contents
- What Hereditary Angioedema Is
- SERPING1, F12, PLG, and Other HAE Genes
- Who Should Consider Genetic Testing
- How Testing Is Done
- Understanding Positive, Negative, and Uncertain Results
- Inheritance and Family Testing
- Diagnosis, Complement Tests, and Limitations
- Treatment and Next Steps
What Hereditary Angioedema Is
Hereditary angioedema, or HAE, is a rare disorder that causes sudden episodes of swelling in the deeper layers of skin or the lining of internal organs. The swelling is usually driven by bradykinin, a signaling molecule that makes blood vessels leak fluid into surrounding tissue.
Common sites include:
- Hands, feet, arms, legs, face, and genitals
- The abdomen and intestinal wall
- The tongue, throat, and upper airway
Skin swelling is often asymmetric, nonpitting, and painful or tight rather than itchy. Abdominal attacks can cause severe cramping, vomiting, diarrhea, and fluid shifts. They may resemble appendicitis, bowel obstruction, or another surgical emergency. Airway swelling can progress unpredictably and may be fatal without rapid treatment.
Attacks often develop over several hours and last two to five days if untreated, though timing varies. Triggers may include dental work, surgery, minor trauma, emotional stress, infection, estrogen exposure, and certain blood-pressure drugs called angiotensin-converting enzyme inhibitors. Many attacks have no obvious trigger.
Classic HAE generally does not cause hives. Antihistamines, corticosteroids, and epinephrine, which work for many allergic reactions, usually do not stop bradykinin-mediated swelling. Emergency clinicians may still give them when the cause is uncertain, because allergic anaphylaxis must be treated promptly and the conditions can initially look similar.
Some patients experience a warning rash called erythema marginatum. It is flat, nonitchy, and often forms pale or red rings before an attack. It can be mistaken for hives.
Symptoms often begin in childhood or adolescence and may worsen around puberty. The frequency ranges from rare lifetime attacks to several episodes per month. People in the same family can have very different severity, and a parent with mild disease can have a child with serious airway attacks.
SERPING1, F12, PLG, and Other HAE Genes
HAE is grouped partly by C1 inhibitor measurements and partly by genetic cause.
SERPING1-related HAE
SERPING1 provides instructions for C1 inhibitor, a protein that restrains several enzyme systems in blood, including the contact pathway that generates bradykinin. Pathogenic SERPING1 variants cause HAE with C1 inhibitor deficiency or dysfunction.
Two traditional laboratory types are recognized:
- HAE type I: C1 inhibitor protein level is low and function is low. This accounts for most SERPING1-related cases.
- HAE type II: C1 inhibitor amount may be normal or high, but its function is low.
Hundreds of SERPING1 variants have been reported, including single-letter substitutions, small insertions or deletions, splice changes, and larger deletions or duplications. A complete analysis may therefore require both sequencing and copy-number testing.
F12-related HAE
F12 encodes coagulation factor XII, which participates in the contact system. Certain gain-of-function variants increase bradykinin generation. F12-related HAE usually has normal C1 inhibitor level and function.
Symptoms are often strongly influenced by estrogen. Some people first develop attacks during pregnancy, while taking estrogen-containing contraception, or with hormone replacement. Females are more often symptomatic, but males can carry a pathogenic variant and occasionally have symptoms.
PLG-related HAE
PLG encodes plasminogen. A recurrent pathogenic variant, commonly described as p.Lys330Glu using current protein numbering, is associated with HAE and normal C1 inhibitor. Tongue and facial swelling are prominent in many reported families, and airway involvement can occur.
PLG-related disease illustrates why a normal C4 and normal C1 inhibitor result do not always end the evaluation. The diagnosis may depend on a characteristic clinical pattern and molecular testing.
Other genes
Pathogenic variants have also been reported in ANGPT1, KNG1, MYOF, and HS3ST6. These genes affect vascular stability, bradykinin pathways, or endothelial signaling. The evidence and number of known families vary by gene.
Some people have familial, antihistamine-resistant, bradykinin-like angioedema with normal C1 inhibitor but no identified pathogenic variant. This is sometimes classified as HAE of unknown genetic cause. Future research may identify additional genes or noncoding variants.
A multigene panel can assess several known causes at once. The exact gene list should be checked because laboratories update panels at different times. A broad genetic panel may also report uncertain variants that are difficult to interpret.
Who Should Consider Genetic Testing
Genetic testing is most informative when the clinical and laboratory evaluation suggests hereditary bradykinin-mediated angioedema.
Testing may be considered for a person with:
- Recurrent swelling without hives, especially when antihistamines do not work
- Repeated unexplained abdominal attacks
- Laryngeal, tongue, facial, or genital swelling without a clear allergic trigger
- Low C4 and low C1 inhibitor level or function
- Normal C1 inhibitor tests but a strong family history or estrogen-sensitive attacks
- A close relative with a known pathogenic HAE variant
- Symptoms beginning in childhood or adolescence
- Suspected HAE that needs distinction from an acquired C1 inhibitor deficiency
For typical low-C1-inhibitor HAE, diagnosis can often be established through complement testing without genetics. Genetic testing becomes especially useful when laboratory results are borderline, the patient is very young, family testing is planned, or acquired angioedema is a concern.
In HAE with normal C1 inhibitor, genetic testing has a larger diagnostic role because routine complement measurements may be normal. A known disease-causing F12, PLG, or other established variant can provide molecular confirmation.
Children in a family with HAE should be evaluated early because the first attack can involve the airway. Complement levels in infants can be difficult to interpret, and testing may need to be repeated after age one. When a familial variant is known, targeted genetic testing can clarify status at any age.
Testing is less useful when swelling always occurs with itchy hives and responds completely to antihistamines. Chronic spontaneous urticaria, food allergy, medication allergy, mast-cell disorders, and anaphylaxis usually follow a histamine pathway. Still, a patient can have both hives and a separate angioedema disorder, so specialists examine the entire pattern.
A first episode after starting an ACE inhibitor may represent drug-induced bradykinin angioedema rather than inherited disease. Acquired C1 inhibitor deficiency tends to begin later in life, lacks a family history, and can be associated with lymphoproliferative or autoimmune disease. C1q testing and clinical evaluation help distinguish it from hereditary disease.
How Testing Is Done
Genetic testing usually uses blood or saliva. No fasting is required. The sample can be collected when the patient is well; a swelling attack is not necessary because inherited DNA does not change between attacks.
A common diagnostic sequence is:
- Document the swelling pattern, medication exposure, family history, and treatment response.
- Measure C4, C1 inhibitor antigen level, and C1 inhibitor function.
- Repeat abnormal or borderline complement results in a qualified laboratory.
- Test SERPING1 when C1 inhibitor deficiency or dysfunction is suspected.
- Use a normal-C1-inhibitor HAE panel when complement tests are normal but inherited disease remains likely.
- Test relatives for the exact familial variant when one is found.
SERPING1 analysis should generally include sequencing plus deletion-and-duplication analysis. Sequencing detects many small variants, while copy-number testing finds missing or duplicated exons and larger rearrangements. Some difficult cases may require RNA analysis, genome sequencing, or another advanced method.
Normal-C1-inhibitor panels vary. They may include F12, PLG, ANGPT1, KNG1, MYOF, and HS3ST6. Before ordering, confirm that the laboratory includes the genes relevant to the patient’s ancestry and clinical picture and that it has a process for reanalyzing uncertain findings.
Results are usually classified as pathogenic, likely pathogenic, uncertain significance, likely benign, or benign. A diagnostic genetic test result should state the DNA change, protein effect when known, zygosity, evidence used, and limitations of the assay.
Turnaround time commonly ranges from two to eight weeks. Targeted testing for a known familial variant may be faster. Emergency treatment should never wait for genetic confirmation.
Genetic counseling can help before and after testing. Important topics include autosomal dominant inheritance, incomplete penetrance, variable severity, testing of children, reproductive options, insurance and privacy rules, and the possibility that a panel returns a VUS rather than a clear answer.
Understanding Positive, Negative, and Uncertain Results
Pathogenic or likely pathogenic SERPING1 variant
A disease-causing SERPING1 variant strongly supports HAE due to C1 inhibitor deficiency or dysfunction, especially when C4 and C1 inhibitor results agree. Most affected people have one altered copy, called a heterozygous variant.
The variant does not precisely predict attack frequency, airway risk, age at onset, or treatment needs. Even relatives with the same variant can have different disease courses. Management should follow the person’s attacks, access to emergency therapy, and quality-of-life impact.
A pathogenic SERPING1 finding can also help distinguish inherited HAE from acquired C1 inhibitor deficiency. However, a new variant still requires careful classification; not every rare SERPING1 change is harmful.
Pathogenic F12, PLG, or other normal-C1-inhibitor HAE variant
A pathogenic variant in an established gene supports a specific HAE subtype when the symptoms are compatible. Penetrance may be incomplete, meaning some carriers never develop attacks. Hormonal exposure can strongly affect expression, particularly in F12-related disease.
A positive result in an asymptomatic relative identifies susceptibility, not certainty about future symptoms. The relative should receive education about airway emergencies, triggering medicines, and when to seek specialist care.
Variant of uncertain significance
A VUS means current evidence cannot determine whether the variant causes disease. It should not be treated as confirmation of HAE. The diagnosis must continue to rest on complement tests, symptoms, family segregation, and response to appropriate therapy.
Testing affected and unaffected relatives may sometimes help, but family testing should be directed by genetics professionals. A VUS found in several symptomatic relatives can add evidence, while its presence in many older unaffected relatives may argue against a highly penetrant cause. Neither observation is always decisive.
Variant classifications can change. Keep the original report and ask the laboratory or ordering clinician about periodic reanalysis.
Negative result
A negative result means the assay did not find a reportable disease-causing variant in the genes and variant types it assessed. It does not completely exclude HAE.
In suspected SERPING1-related disease, a negative result may reflect a deep intronic variant, complex structural change, mosaicism, or a technical limitation. Repeated low C4 and low C1 inhibitor function can still establish the clinical diagnosis.
In HAE with normal C1 inhibitor, many families remain genetically unexplained. A negative panel may therefore lead to a clinical diagnosis of HAE of unknown cause after allergic, drug-induced, and acquired forms have been carefully excluded.
Benign or likely benign result
A benign variant is not considered a cause of HAE. Common polymorphisms should not be used to diagnose disease, predict attacks, or test relatives. Direct-to-consumer raw data may contain genotyping errors and usually lacks the comprehensive coverage needed for HAE diagnosis; clinically important findings need confirmation in an accredited laboratory.
Inheritance and Family Testing
Most known forms of HAE follow an autosomal dominant pattern. A person with a pathogenic variant in one gene copy has a 50% chance of passing that variant to each child. The probability is the same in every pregnancy, regardless of sex.
About one quarter of people with SERPING1-related HAE may have a new, or de novo, variant rather than an affected parent. Once the variant occurs, it can be passed to future generations. Absence of family history therefore does not rule out HAE.
Variable expressivity means severity differs among carriers. Incomplete penetrance, especially in some normal-C1-inhibitor forms, means a carrier may never develop recognizable symptoms. These features make symptom-only family screening unreliable.
When a pathogenic familial variant is known, targeted testing is usually the clearest way to evaluate relatives. It is less expensive and easier to interpret than repeating a full panel. Relatives who test positive can receive an emergency plan and access to treatment before a first severe attack.
When no familial variant is known but C1 inhibitor deficiency is confirmed, first-degree relatives should have C4, C1 inhibitor antigen, and functional testing. Normal results may need confirmation, particularly in young children.
Reproductive options can include natural conception with postnatal testing, prenatal diagnosis, or preimplantation genetic testing. The decision is personal. HAE severity is unpredictable, and effective treatment is available, so counseling should be balanced and nondirective.
Pregnancy requires specialized planning. Estrogen can worsen some forms, while attack patterns may improve, worsen, or stay unchanged. Certain treatments are preferred during pregnancy and breastfeeding. Patients should discuss prophylaxis for delivery and access to on-demand treatment well before labor.
Diagnosis, Complement Tests, and Limitations
Genetic testing is one part of the diagnostic system. For suspected C1 inhibitor deficiency, the core laboratory tests are C4, C1 inhibitor antigen level, and C1 inhibitor functional activity.
C4 is often low between attacks and usually falls further during attacks, but a normal C4 does not absolutely exclude HAE. C1 inhibitor quantity distinguishes many type I cases, while functional testing identifies type II disease. Samples must be handled correctly because poor transport or storage can distort functional results.
C1q can help when acquired angioedema is suspected. It is often low in acquired C1 inhibitor deficiency and usually normal in hereditary disease, though exceptions occur.
The differential diagnosis includes:
- Histamine-mediated allergy or anaphylaxis
- Chronic spontaneous urticaria with angioedema
- ACE inhibitor or neprilysin inhibitor-associated angioedema
- Acquired C1 inhibitor deficiency
- Idiopathic nonhistaminergic angioedema
- Contact reactions, cellulitis, venous obstruction, and other causes of localized swelling
- Gastrointestinal, gynecologic, or surgical causes of recurrent abdominal pain
Clinical response provides clues. Bradykinin-targeted medicines can stop HAE attacks, whereas high-dose antihistamines are more effective for mast-cell-mediated swelling. Response alone is not a perfect diagnostic test because attacks can resolve spontaneously.
Genetic panels have important limitations. They may omit newly discovered genes, miss deep intronic or structural variants, report uncertain findings, or identify a variant whose penetrance is poorly defined. The gene-disease relationship for rare reported genes may strengthen or change over time.
Misclassification can have serious consequences. An incorrect HAE diagnosis may expose a person to expensive treatment and distract from allergy, medication effects, or another illness. Missing true HAE can leave a person unprepared for airway swelling. Specialist review is therefore essential, especially when complement and genetic results disagree.
Treatment and Next Steps
Every person with confirmed or strongly suspected HAE should have a written emergency plan and access to effective on-demand treatment. Airway symptoms take priority over every test result.
On-demand therapies may include a bradykinin B2 receptor antagonist, a plasma kallikrein inhibitor, or C1 inhibitor concentrate, depending on country, age, subtype, and availability. Patients and caregivers can often be trained to treat at home early in an attack. Emergency evaluation is still required for tongue or throat swelling because airway management may be needed.
Short-term prophylaxis may be used before dental work, surgery, intubation, or another procedure that could trigger swelling. Long-term prophylaxis may be considered for frequent attacks, severe past attacks, poor access to emergency care, or major quality-of-life impact. Options include regular C1 inhibitor replacement, kallikrein-targeted medicines, and other approved therapies.
After a positive genetic result:
- Confirm how the result fits complement studies and symptoms.
- Create an emergency action plan and carry medical identification.
- Obtain on-demand medicine and learn how to use it.
- Review medications, especially estrogen and ACE inhibitors.
- Discuss procedure-related prophylaxis.
- Offer targeted testing to appropriate relatives.
- Review attack control regularly with an HAE specialist.
After a negative result, do not stop the evaluation if the clinical pattern remains convincing. Confirm which genes and variant types were tested, repeat complement studies if needed, and consider expert review or advanced testing. A specialist may classify the condition clinically and arrange treatment while the genetic cause remains unknown.
After a VUS, avoid using the result as the sole reason for diagnosis or family labeling. Continue objective clinical assessment and request reanalysis over time.
Keep a record of swelling location, onset, duration, possible trigger, menstrual or pregnancy timing, treatment, and response. Photographs of external swelling and emergency records from abdominal attacks can help. Note whether hives were present and whether antihistamines worked.
Call emergency services immediately for voice change, trouble swallowing, drooling, tongue swelling, throat tightness, noisy breathing, or shortness of breath. Use prescribed on-demand treatment at once, but do not delay emergency airway care while waiting to see whether symptoms improve.
Genetic results should be read beside complement testing and attack history. Low C4 with reduced C1 inhibitor antigen or function strongly supports C1-inhibitor-deficient hereditary angioedema, while normal values between attacks do not resolve every normal-C1-inhibitor form. A pathogenic variant can clarify family screening, but emergency treatment should not wait for sequencing when airway swelling is suspected. Relatives who test positive still need an individualized action plan, access to on-demand therapy, and education about procedures, estrogen exposure, and other personal triggers.
References
- Hereditary Angioedema with Normal C1 Inhibitor: an Updated International Consensus Paper on Diagnosis, Pathophysiology, and Treatment 2025 (Consensus)
- Expanding the Genetic and Clinical Spectrum of Hereditary Angioedema With Normal C1 Inhibitor 2025
- Hereditary or acquired? Comprehensive genetic testing assists in stratifying angioedema patients 2024
- Identification of 12 novel variants in SERPING1 gene 2024
- Phenotypic and molecular characterization of the largest worldwide cluster of hereditary angioedema type 1 2024
- The international WAO/EAACI guideline for the management of hereditary angioedema-The 2021 revision and update 2022 (Guideline)
Disclaimer
This article provides general information and cannot diagnose hereditary angioedema or select treatment for an individual. Genetic results must be interpreted with complement studies, symptoms, family history, and specialist assessment. Tongue, throat, voice, swallowing, or breathing symptoms are emergencies and require immediate treatment and emergency medical care.
