Take part in the STOP-HAE clinical trial
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A new study examining the reality of HAE

If you’re living with hereditary angioedema (HAE), you may know the impact it can have on everyday life. From sudden, swelling attacks to never knowing when the next one will be, its unpredictable challenges may make you feel like you’re losing control.

The siRNA Targeting of Prekallikrein for Hereditary Angioedema (STOP-HAE) clinical trial is here to help discover additional treatment options. It explores an investigational drug called ADX-324 – a small interfering RNA (or siRNA) that blocks cells in the body from producing a protein called prekallikrein (PKK), which plays a critical role in HAE attacks. Therefore, ADX-324 may help prevent HAE attacks from starting and could make the ones that do start, less frequent and severe. Because it may be given every three or six months, ADX-324 has the potential to offer you longer periods of time between treatments and fewer, less severe HAE attacks.

By exploring what’s possible in long-term HAE management, we’re exploring options to give you and others like you the chance to finally move forward.

What is STOP-HAE?

STOP-HAE is a clinical study that aims to find new ways to manage HAE. It explores how the investigational drug ADX-324 may help prevent attacks before they happen, and to evaluate whether ADX-324 may reduce the frequency and severity when they do.

The study is helping researchers to evaluate ADX-324 for its safety and efficacy, as well as how much of a difference it makes on participants’ quality of life. By taking part in this clinical study, you could learn more about managing your HAE symptoms and help others like you begin their own journey too.

What is ADX-324?

ADX-324 is a siRNA that targets prekallikrein (PKK) – a protein that plays a critical role in HAE attacks. ADX-324 blocks cells in the body from producing this protein, which may help to prevent an attack before it begins and could make the ones that do start less frequent and severe. It’s important to note that ADX-324 is not a gene-therapy and does not change a person’s DNA.

What makes ADX-324 and the STOP-HAE study unique?

Current treatments for HAE are usually taken frequently, either as a daily pill or an injection every 1 to 2 weeks. Over time, this can feel burdensome for an individual, and could be dangerous, if the treatment is forgotten or missed.

ADX-324 comes as subcutaneous injection which means it’s injected under the skin. It is administered every 3 or 6 months, potentially helping to make managing HAE simpler by requiring fewer doses compared to current treatments. 

Can I take part?

To take part in the STOP-HAE clinical study, you must be:

  • At least 18 years old
  • Be diagnosed by a physician with HAE Type I or Type II
  • Be willing to stop any long-term, preventative medication used to prevent attacks
  • Have access to at least one acute therapy that has worked for you before
  • Have no significant medical history that could interfere with the study (for example, hypertension, diabetes or cardiovascular disease)
  • Be able to provide written informed consent and be willing to comply with all study required procedures for the duration of the study (such as completing a daily eDiary)
  • Have a mobile phone to register and set up your eDiary account (once registered, you may complete your daily eDiary updates using your computer or tablet). If you cannot update the eDiary regularly, it may affect your ability to remain in the trial.

Please note that this is not a full list of requirements. Your doctor will assess your eligibility with you. Your study doctor will be able to answer any questions for you and will be there to support you throughout the screening, treatment and end-of-study period.

What to expect

Screening – 4 to 8 weeks

Before we start any tests or procedures, you will be provided a consent form for the primary study, ADX-324-301. You will be given time to review the form, ask your doctor questions, and discuss with family members, if needed. If you decide to participate, you will be asked to sign the consent form. Our trial doctors will then ask you some questions and complete a full evaluation to determine whether you meet all study requirements and are eligible to participate. Once you have provided your consent and your questions are answered, you may begin participating in the study.

Our trial doctors will then ask you some questions and complete a full evaluation to determine whether you meet all study requirements and are eligible to participate. Once you have provided your consent and your questions are answered, you may begin participating in the study.

Before any study-related tests and procedures are performed, you will be asked a few questions about long-term prevention medications for HAE. Your answers will help the study doctor determine if a “washout period” (the time to taper off the medication and eventually totally stop taking it) is needed and how long it should be. You will also be asked to read and sign a consent document. During the washout period, you will be asked about any HAE attacks that happened during this time.

Once the washout period is complete (if applicable), you will have a Screening Visit. At this visit, the study doctor will ask you some questions, and some screening tests and procedures will be performed to determine if you meet the requirements to be in this study. This study visit may take several hours.

This screening period will also include completing quality of life (QoL) questionnaires, using a daily eDiary to report HAE attacks, should these occur, and basic medical tests, such as:

  • Measurement of vital signs (blood pressure, breathing rate, heart rate, and temperature)
  • Electrocardiogram (ECG) heart test
  • Blood and urine sample collection
  • Questions about your QoL, current HAE symptoms, any medications you have taken recently or are currently taking and medical history

You’ll also learn how to use the study app and eDiary which will be used to track HAE attacks throughout the duration of the study. Your trial doctor and study team will teach you how to use this during your screening visit.

Study and follow-ups – 25 weeks

If you qualify to take part, you’ll be randomly assigned to one of three groups:

  • Those taking ADX-324 at a higher dose (300mg)
  • Those taking ADX-324 at a lower dose (240mg)
  • Those taking a placebo (saline solution)

During the study, you will receive the relevant injection for your group. You will not know which group you are assigned to. Depending on your dosing schedule, you may only have to receive one dose of the investigational drug in this period.

No matter which group you’re in, you’ll have our full support during the trial duration. The trial doctors will monitor you all the way through with regular clinic or office appointments, physical assessments, questionnaires and follow-ups to see how you’re feeling.

These assessments may include:

  • Physical examination
  • Measurement of vital signs (blood pressure, breathing rate, heart rate, and temperature)
  • Blood and urine sample collection
  • Additional blood tests to see how your body is reacting to the study drug
  • ECG heart test
  • HAE attack assessment to check the frequency and severity of your attacks should you be experiencing HAE attacks
  • Questionnaires about symptoms you may or may not be experiencing, quality of life and medications you are taking

While in the study, participants who choose to take part may be able to also opt-in to having home nursing visits if your trial doctor agrees. On-demand, rescue medications taken for HAE attacks by participants during the study (including the screening period) may be reimbursed (if allowed by regulatory authorities) while enrolled.

Optional extension study – up to 3 years

Once you’ve completed the study, you are eligible to participate in an extension study, ADX-324-302, where all participants will receive the investigational drug, ADX-324. This means that if you were on the placebo, you would now be assigned to a ADX-324 treatment group, whereas those already on treatment would continue the same dose as before. All participants will receive ADX-324 at no cost. Should you end participation early in the primary study, you will not be eligible to participate in the extension study.

If you decide to participate in the optional extension study, ADX-324-302, also known as the STOP-HAE Extension Study, you will receive the investigational drug, ADX-324, for up to an additional 3 years. The eDiary will be used to continue to track your HAE attacks throughout the extension study.

Take part in the STOP-HAE clinical trial

FAQs

Why should I take part in STOP-HAE?

STOP-HAE is a clinical research study aiming to potentially find new ways to manage type I and type II HAE in adults (age 18 and over).

Ultimately, it’s up to you whether you want to participate. But if you do, you would be a key part of making advancements in HAE treatment and potentially helping to improve the lives of others like you.

Are there any risks?

As with all clinical studies, there are possible risks. Your doctor will inform you what they are before you give consent to participate in the study. You’ll have the care of your research team who will closely monitor your health throughout the study duration.

Can I continue to take my rescue medication?

Yes. You will be able to take your on-demand, rescue medication if you experience an attack. We’ll only ask that you document all HAE attacks in the eDiary and the medication you take for these attacks during your study period.

Are there any costs?

No. Participants will receive all study-related procedures and the investigational drug at no personal cost. You will be responsible for your normal healthcare costs. Patient out-of-pocket expenses related to participation in the study, such as travel and accommodations, may be covered per country and local regulations. Please speak with your physician for further details.

How long will the study last?

The initial study, STOP-HAE, will take approximately 7-8 months to complete. Upon completion, you may be eligible to participate in an optional extension study which could last up to 3 years.

Take part in the STOP-HAE clinical trial

November 2025 Hereditary Angioedema Association (HAEA)’s Treatment Education Series

The November 2025 Hereditary Angioedema Association (HAEA)’s Treatment Education Series featured a webinar about ADX-324 and the STOP-HAE study called, “ADX-324 (siRNA): Advancing HAE Care and Next Generation Treatments”. The session covered common questions that STOP-HAE participants may have, and details around how siRNA therapies are intended to work and what potentially makes ADX-324 different from other preventative treatment options. Watch below to learn more.