Hereditary hemorrhagic telangiectasia, usually shortened to HHT, is an inherited condition in which some arteries connect straight into veins instead of passing through the tiny vessels in between, creating fragile spots that bleed easily and abnormal connections that can form inside the lungs, brain and liver [1,3].
This page provides general information. It does not replace advice from a doctor or another qualified healthcare professional.
Blood normally leaves the heart through arteries at high pressure, slows through capillaries, the extremely small vessels that pass oxygen to the tissues, then returns through veins at low pressure [3].
In HHT some arteries join veins directly, with no capillaries in between [1,3]. Small ones show as red or purple spots under the skin or the lining of the nose, mouth and gut, and are called telangiectases [3,4]. Larger ones, up to several centimeters across, are arteriovenous malformations, or AVMs [1].
They bleed because the capillaries are missing. High-pressure blood arrives straight into a thin-walled vein never built for it, so the join stretches and turns fragile [3]. These vessels sit close to the surface and lack the muscle that lets a normal vessel clamp down, so bleeding is brisk and hard to stop [1].
HHT is also called Osler-Weber-Rendu disease. Spots on the lips, mouth and fingers are what separate it from look-alike conditions [1,7].
The usual figure is about 1 in 5,000, counting people with a clinical diagnosis [1,2]. MedlinePlus Genetics gives 1 in 5,000 to 1 in 10,000, and the main United States patient organization uses 1 in 4,000 [3,5].
Experts agree the real figure is higher, since HHT is underdiagnosed and long delays are common [2]. Counting is hard: severity varies, nosebleeds are common generally, and AVMs occur for other reasons too [3].
Work published in 2026 across three large population genomic databases found 1.75 to 2.56 people per 5,000 carrying a known disease-causing change in one of the two main genes [11]. Those figures count variant carriers, not people who know they have HHT.
HHT occurs worldwide in many ethnic groups, with higher local rates in parts of France and on Curaçao and Bonaire [1,3].
Genes are the instructions a body uses to build proteins. Three genes account for most HHT: ENG, ACVRL1, also written ALK1, and SMAD4, and all three make proteins in the lining of blood vessels that guide how vessels form [1,3,5].
HHT is inherited in an autosomal dominant pattern. Everyone carries two copies of each gene, and one altered copy is enough, so each child of a person with HHT has a 50 percent chance of inheriting it, whatever their sex, and nearly everyone inherited it from a parent [3,5].
The condition also shows age-related penetrance. The gene change is present from birth, yet signs appear gradually: nosebleeds usually in late childhood, spots in early adulthood, and almost everyone who carries the change has signs by late adulthood [1,7]. A parent who seems unaffected may not show it yet, and a child who looks well cannot be assumed clear [1,2]. Nothing a person did caused HHT.
Nosebleeds and telangiectases each affect around 95 percent of people with HHT, anemia about half, lung AVMs 30 to 50 percent, liver AVMs 40 to 70 percent and brain AVMs around 10 percent, all age-related [1].
Nosebleeds. The commonest feature and usually the most burdensome. They begin at an average age of 12, and about 90 percent of people have them by age 30 [1]. They range from a few times a year to several times a day, and many never need treatment [1].
Red or purple spots. Pinpoint to pinhead in size, usually on the lips, tongue, fingertips, inside the mouth, and the lining of the nose and gut [1,4].
Iron deficiency anemia. Repeated blood loss uses up the body’s iron, causing tiredness and breathlessness, with gut bleeding a bigger contributor after age 50 [1].
Silent AVMs, the most important point on this page. Lung and brain AVMs frequently cause no symptoms at all, and are still dangerous. When blood bypasses the filtering action of the lungs, air bubbles, clots and bacteria can travel straight to the brain, causing stroke or a brain abscess in someone who feels completely well [1]. Screening is recommended precisely because these AVMs are silent, and symptoms can begin at any age [1,2,7].
When to seek urgent help. Get emergency medical help for a nosebleed that will not stop despite firm pressure, for a sudden severe headache or any sudden neurological change such as weakness, confusion, difficulty speaking or seeing, a seizure or loss of consciousness, and for coughing up blood [1,4]. Tell the emergency team you have HHT and mention any known lung AVM.
Most people start with a family doctor, then see ear, nose and throat surgeons, blood specialists and genetics teams, ideally at a center that treats HHT regularly [1,2].
Diagnosis is usually clinical, using the four Curaçao criteria published in 2000 [6]:
HHT is definite with three or more criteria, possible with two, and unlikely with fewer than two [1,6]. Guidelines say to diagnose it this way or by finding a causative gene change, and genetic testing identifies the change in a family so relatives with no symptoms can be tested [1,2]. The criteria often miss affected children, so a child of a parent with HHT is treated as possibly affected unless testing rules it out [1,2].
Screening then follows: a blood count and ferritin level, a contrast echocardiogram to detect blood bypassing the lungs, a brain MRI, and liver imaging in adults [1,2].
There is no cure. Most telangiectases and AVMs can be treated once they appear, and much of the work is preventing complications [4,5].
Nosebleeds, step by step. Humidifying and moisturizing the nasal lining twice a day comes first [1,2]. Next is oral tranexamic acid, a medicine that helps clots hold together [2]. Then treatments that seal the vessels in the nose: laser, radiofrequency ablation or injection therapy [2]. Then medicines that act on blood vessel growth, with surgery kept for severe cases and needing surgeons who regularly treat HHT [1,2].
Medicines that act on blood vessel growth. Intravenous bevacizumab is recommended for nosebleeds and gut bleeding that have not responded to earlier steps, and for heart strain from liver AVMs [2]. Pomalidomide and pazopanib are used for bleeding that resists other treatment [1]. All are used off label, and no medicine is licensed specifically for HHT anywhere in the world [1,9].
Iron and anemia. All adults with HHT are tested for iron deficiency and anemia whether or not they have symptoms, with tablets first and iron into a vein if tablets do not work [2].
Lung AVMs. These are closed by transcatheter embolization, where a small plug is placed through a fine tube to block the feeding artery [2,4]. It is advised for any lung AVM with a feeding artery around 2 to 3 mm or wider, chiefly to prevent stroke and brain abscess, even when oxygen levels are normal [1]. Treated AVMs can reopen, so follow-up imaging matters [1,2].
Brain and liver. Brain AVMs are treated by surgery, embolization or targeted radiotherapy, and lower-risk ones are often left alone [1,4]. Liver AVMs are managed with medicines, not embolization [1,2].
Two things to tell every healthcare professional, if you have a lung AVM or blood bypassing your lungs. First, you need antibiotics before dental cleaning and other procedures that can push bacteria into the blood, since those bacteria can skip the filter the lungs provide and settle in the brain [1,2]. Second, anyone putting a drip or line into a vein must keep air bubbles out, using an air filter where one is available [1,2]. This saves lives, and staff treating you in an emergency may not know it, so carry it in writing.
Everyday measures and review. Keep the air humid, moisturize the nose twice daily, and avoid vigorous nose blowing, heavy lifting and straining [1]. Aspirin and ibuprofen-type medicines are usually avoided where bleeding is significant, as is liver biopsy [1]. Expect an annual check with an HHT-aware clinician, a yearly blood count and ferritin level, and repeat imaging as your team advises [1].
Family and pregnancy. Relatives can be offered testing, best discussed before trying to conceive [1,2,5]. Tell your maternity team early, since lung AVMs are screened for and treated from the second trimester [2].
SMAD4-related HHT. Where the change is in SMAD4, HHT overlaps with juvenile polyposis, meaning growths form in the gut, so bowel surveillance is added: colonoscopy from age 15, repeated every three years if nothing is found, or yearly with an upper endoscopy if polyps are seen [1,3].
Unpredictable nosebleeds and constant tiredness wear people down, and national HHT associations exist for this [14].
Clinical trials test whether a treatment works and is safe. HHT has no licensed medicine yet, so trials matter here [1,9,10]. Deciding whether to look into one is personal, and it helps to take it in steps.
It is worth being clear on what a study involves:
Every trial has rules about who can take part, called eligibility criteria. For an HHT study they might include a diagnosis confirmed by the Curaçao criteria or by genetic testing, nosebleeds above a set frequency or severity score, a hemoglobin or ferritin level in a given range, and reliable contraception for medicines that could harm a baby.
trialport’s medifit helps people consider information related to possible medical suitability. It does not diagnose a condition, confirm eligibility or replace formal screening by the study team.
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In the United States, Cure HHT is the main condition-specific organization, with plain-language explanations and a directory of HHT centers [5].
In Europe, VASCERN’s HHT Working Group brings together and maps expert centers across the European Reference Network for rare vascular conditions [13].
In the United Kingdom, the Telangiectasia Self Help Group has connected families since 1985 [15], and the NHS page on HHT is a short overview [4].
Cure HHT keeps a directory of national patient associations covering fourteen countries in Europe, the Americas, Japan and Israel [14]. It lists no group in Australia, New Zealand, Africa, or most of Asia and the Middle East [14].
Is HHT serious?
It varies. Many people manage with moisturizing treatment and iron, while others face heavy bleeding or complications from AVMs [1,4]. Screening prevents much of the harm [2].
Do I need scans if I feel completely well?
Yes. Lung and brain AVMs commonly cause no symptoms while still carrying a risk of stroke and brain abscess, so screening is advised for everyone with possible or confirmed HHT [1,2].
Can my children inherit it?
Each child has a 50 percent chance, regardless of sex [3,5]. Signs appear at different ages, so a child with no symptoms is treated as possibly affected until testing says otherwise [1,2].
Why do I need antibiotics before the dentist?
If blood bypasses your lungs through an AVM, bacteria stirred up during dental work can reach the brain instead of being filtered out [1,2].
Why did it take so long to get diagnosed?
HHT is underdiagnosed and long delays are common [2]. Nosebleeds happen to plenty of people, so families with several affected members often assume it is normal [3].
Written by: trialport editorial team
Reviewed by: Keith Berelowitz, Founder and CEO, trialport
Reviewed on: 3 August 2026
Next review due: 3 August 2027
References last checked: 3 August 2026