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Diseases Studied

The Rare Diseases Clinical Research Network is an NIH-funded research network of 20 active consortia or research groups working to advance treatment for diseases that are rare. Use the search tools on this page to find the diseases we currently study. You can reach out to the indicated consortia or research groups for more information on those diseases and studies underway.

This network focuses on clinical research and does not generally support clinical care outside of research activities. To learn about other rare diseases, please visit the Genetic and Rare Diseases Information Center (GARD), which is an NIH program that helps the public find reliable information about rare and genetic diseases. Their staff are specialists. Contact them at 1-888-205-2311 or email

All Diseases > Hereditary Hemorrhagic Telangiectasia

Hereditary Hemorrhagic Telangiectasia (HHT)

Alternative Names: Brain Arteriovenous Malformation (BAVM)

Disease Category: Brain Vascular Malformations

A rare inherited disease with an estimated prevalence of 1 in 5000, characterized by abnormal blood vessels. HHT is caused by mutations in three known genes; Endoglin (ENG), Activin A Receptor Like Type 1 (ACVRL1) and SMAD4, with dominant inheritance. The abnormal blood vessels consist of direct artery to vein connections, with the small ones called telangiectasia and the large ones called arteriovenous malformations (AVMs). Most patients have telangiectasia on the lining of the nasal passages and/or the gastro-intestinal tract, resulting in chronic bleeding and anemia. At least 50% will also have AVMs in the internal organs (commonly in the lung, liver, brain) which can lead to life-threatening hemorrhage, stroke, heart failure and liver disease.

Research groups studying this disease

Brain Vascular Malformations
BVMC logo

Brain Vascular Malformation Consortium (BVMC)


To identify predictors of brain outcomes in HHT patients. We propose to leverage our multicenter network of HHT Centers to characterize comprehensive brain outcomes. We hypothesize that the presence of BAVMs (vs. HHT patients without BAVMs) and multiplicity of BAVMs will be associated with worsening functional outcome. We will use the modified Rankin Score (mRS) to measure the functional outcome. Furthermore to define a severe bleeding phenotype in HHT for clinical trial readiness. We hypothesize that weekly nasal bleeding duration (Patient-Reported Outcome Cumulative nasal Bleeding duration, or PRO-CB) in HHT will predict the need for invasive or life-sustaining therapies (surgery, urgent packing, blood transfusions, iron infusions). We propose to measure PRO-CB longitudinally in HHT patients and correlate with the need for invasive or life-sustaining therapies (primary outcome), as well as with ICH risk from BAVMs and with bleeding in other HHT organ phenotypes (including pulmonary AVMs and GI telangiectasia).

This pilot study is to determine the safety and efficacy of oral sirolimus (blood trough level 6-10ng/ml) in patients with HHT that are experiencing moderate or severe epistaxis. The effect of oral sirolimus on epistaxis will be compared to baseline using the Patient-Reported Outcome of cumulative weekly nose Bleeding Duration (PRO-CB). The PRO-CB association with biomarker variability over the duration of the study will be investigated. In the pilot study subjects will be treated with 2mg of sirolimus once daily to obtain a trough level of 6-10ng/ml for 3 months.

Supports individuals and families affected by HHT through research, patient/family education, medical education, and treatment centers worldwide.