Hereditary haemorrhagic telangiectasia (HHT) is a genetic condition that affects blood vessel formation. People with HHT develop arteriovenous malformations (AVM). AVM is an abnormal tangle of arteries and veins, due to the absent of capillaries. Capillaries are tiny blood vessels that connect arteries to veins, and deliver oxygen and nutrients to cells. AVM blood vessels are weak and fragile, and can rupture or burst easily. AVM can happen in multiple areas of the body.

A small AVM is known as telangiectasia (“spider veins”), they appear as red, blue or purple blood vessels. Telangiectasia is more common in the skin, lips, fingers, and nose. Individuals with HHT often have frequent nose bleeds.

AVM usually refer to malformation in larger blood vessels, and most commonly affect the brain, spinal cord, lungs, liver, and gastrointestinal tract. This can lead to irregular blood flow, bleeding/haemorrhage, damage to organs, and other serious complications. Symptoms and severity of HHT can vary widely between individuals.

Below on this page is some information about this condition as well as links to useful resources for Australians living with a rare disease.

Synonyms: HHT, Osler-Weber-Rendu disease. Rendu-Osler disease, Rendu-Osler-Weber disease, Osler haemorrhagic telangiectasia syndrome.

Universal rare disease classifications provide a common language for recording, reporting and monitoring diseases. Please visit the Rare Disease Classifications page for more information about these internationally recognised classifications.

ORPHA:774 Hereditary haemorrhagic telangiectasia

ICD-11: LA90.00 Hereditary haemorrhagic telangiectasia

Rare diseases typically display a high level of symptom complexity. There is often a wide range of symptoms and the symptoms may vary between individuals in terms of its presentation, severity, duration and impact.

Please speak to your medical team to learn more about the symptoms of this condition.

Rare diseases are often serious and progressive, exhibiting a high degree of symptom complexity, leading to significant disability. Majority of the estimated two million Australians living with a rare disease meet the Australian Government’s definition for disability (in accordance to the Australian Public Service Commission and Australian Bureau of Statistics), and many experience severe and permanent disability impacts. If you or someone you care for is experiencing disability-related impacts from a rare condition, please speak with a health or disability professional for advice. Information about relevant disability support can be found at the RARE Portal’s Disability Support Information page.

HHT is a genetic condition, caused by disease-causing genetic changes (variants) in at least 3 different genes that code for proteins involved in the development of blood vessels. It is likely that more genetic variants are yet to be discovered.

These genes currently identified are ENG gene on chromosome 9, ACVRL1 gene on chromosome 12., and SMAD4 gene on chromosome 18 (less common). In a small number of individuals, the disease-causing genetic variant has not yet been identified.

All individuals have two copies (alleles) of each gene, one inherited from each parent. HHT is an autosomal dominant condition, which means that having a genetic variant in just one copy of the ENG, ACVRL1, or SMAD4 gene can result in HHT. The genetic variant can be passed on to the next generation. If a parent has the autosomal dominant gene variant, there is a 50% chance that they will pass that genetic variant to each of their children. More information on autosomal dominant inheritance pattern can be found at Centre for Genetics Education: Autosomal dominant inheritance

In rare cases, the genetic variant:

• occurred randomly (de novo) prior to birth and is not passed down from their parents
• was inherited from a parent who has the genetic variants in some but not all of their cells (this is called genetic mosaicism). Parents usually do not show any signs of HHT. More information on genetic mosaicism can be found at Centre for Genetics Education: Mosaicism.

If you would like to learn more about the inheritance and impact of this condition, please ask your doctor for a referral to a genetic counsellor. Genetic counsellors are qualified allied health professionals who can provide information and support regarding genetic conditions and testing. More information about genetic counselling can be found at:

• Information on Genetic Services
• The National and State Services pages underneath the ‘Genetic Counselling’ sections listed

A timely diagnosis is critical for better patient outcomes, the provision of the best possible care and treatment options, access to services and support, increased reproductive confidence and the ability to participate in clinical trials.

Please speak to your medical team to learn more about the available diagnostic pathways for this condition.

Please speak to your medical team to learn more about the possible treatment or management options for your condition. Treatment will depend on an individual’s specific condition and symptoms. It is also important to stay connected to your medical team so that you can be made aware of any upcoming clinical trial opportunities.

Healthcare professionals involved in the treatment of HHT may include general practitioners (GP), paediatricians, haematologists, ear nose throat (ENT) specialists, pulmonologists, genetic counsellors. The need for different healthcare professionals may change over a person’s lifetime and extend beyond those listed here.

Clinical care for rare diseases often involves a multidisciplinary team of medical, care and support professionals. Please note that the information provided here is as a guide and that RVA does not necessarily monitor or endorse specific clinics or health experts.

For many rare diseases, palliative care services may be relevant and useful. Palliative care services are available for people (adults, children and their families) living with a life-limiting illness and is not only for end-of-life care. It can also help at any stage of illness from diagnosis onwards, and will look different for different people. Palliative care services provide assistance, support, resources and tools to help people manage their illness and the symptoms, ease pain, and improve comfort and quality of life. If this is relevant to you and you wish to find out more information about palliative care and how it can help you, please visit:

• Australian Institute of Health and Welfare: Palliative care Overview
• Australian Government Department of Health, Disability and Ageing: Palliative care
• Palliative Care Australia

We are not aware of any clinical care guidelines for HHT in Australia. If you know of any relevant care guidelines, please let us know via the Contribute page.

The following guidance is available from international experts outside Australia; however, there may be information that is not relevant or applicable to the Australian context, and may not be up to date:

Second International Guidelines for the Diagnosis and Management of Hereditary Hemorrhagic Telangiectasia developed by medical experts of HHT from 15 countries, published in 2020.

Individuals living with rare diseases may have complex medical issues and disabilities, which are not always visible. It is often useful to refer to their medical history as well as personal information such as a medical card, doctor’s letter, or if available, a rare disease passport, for relevant information.

If you know of any relevant emergency management guidelines or information relevant to emergency care, please let us know via the Contribute page.

There are specific considerations around participating in rare disease research, including clinical trials. It is important to be mindful of issues such as data privacy, research ethics, consent and differences in research regulations between Australia and other countries. For more information, please visit the RARE Portal’s Considerations for Participating in Health and Medical Research page.

If you are interested in finding clinical trials for your condition, please visit the following websites; however, there may not be any clinical trials available:

• Australian Clinical Trials
• ClinicalTrials.gov

It is best to discuss your interest in research, including clinical trials,  with your medical team to determine suitability and eligibility.

Australian Organisation:
We are not aware of any rare disease organisations for HHT in Australia. If you are aware of any Australian organisations, please let us know via the Contribute page.

International Organisation:
Cure HHT (United States of America)
Website: https://curehht.org/

Please note that RVA does not monitor or endorse each group/organisation’s operational governance and activities. When engaging with a group, please consider the information on the RARE Portal’s Finding Helpful Peer and Community Supports page.

HHT varies between individuals, and each person’s experience is unique.

If you would like to share your personal story with RVA, please visit the Rare Voices Australia: Share Your Story page. RVA will consider your story for publishing on our website and inclusion on the RARE Portal.

For information on available government and social services that provide support for individuals with a rare disease, please visit the National and State Services pages.

People living with a rare disease often face unique challenges such as diagnostic delays, misdiagnoses, limited treatment options, and limited access to rare disease specialists and support. These challenges may impact people’s emotional wellbeing and quality of life. Many find it helpful to seek mental health and wellbeing support to cope with ongoing stress and uncertainty. Connecting with people who have shared experiences through a support group may also be helpful. Information about relevant mental health and wellbeing support can be found at:

• Mental Health and Wellbeing Support for Australians Living with a Rare Disease
• The National and State Services pages underneath the ‘Mental Health’ sections listed

Further information on HHT can be found at:

• Genetic and Rare Diseases (GARD) Information Center: Hereditary hemorrhagic telangiectasia
• National Organization for Rare Disorders (NORD): Hereditary Hemorrhagic Telangiectasia

GeneReviews®: Hereditary Hemorrhagic Telangiectasia

Online Mendelian Inheritance in Man, OMIM®: #187300 Telangiectasia, hereditary hemorrhagic, type 1; HHT1

Online Mendelian Inheritance in Man, OMIM®: #600376 Telangiectasia, hereditary hemorrhagic, type 2; HHT2

Online Mendelian Inheritance in Man, OMIM®: #610655 Telangiectasia, hereditary hemorrhagic, type 4; HHT4

Orphanet: Hereditary haemorrhagic telangiectasia

Human Phenotype Ontology (HPO): Hereditary haemorrhagic telangiectasia

This page has been developed by Rare Voices Australia (RVA)’s RARE Portal team. If you would like to see more information added to this page, please reach out via the Contact form. If you would like to share relevant resources for this condition, please visit the Contribute page.

If you are aware of any additional information that may benefit stakeholders with an interest in this page, or if you notice any broken links or inaccurate information, please let us know via the Contribute page.