Start with the clinical question in front of you.
Recurrent nosebleeds. Iron deficiency that keeps coming back. A family history nobody connected. An incidental AVM on imaging. HHT tends to arrive in clinic disguised as something more ordinary, and the pattern is easier to recognize once you have seen it laid out.
Five things to know
From suspicion to a plan
About 80% of people with HHT are undiagnosed, and the average delay from first symptoms to diagnosis is 27 years. Most of that delay is not diagnostic difficulty. It is that nobody counted the findings together.
1
Recognize the pattern
Spontaneous recurrent epistaxis, mucocutaneous telangiectases at characteristic sites, visceral AVMs or VMs, and a first-degree relative with HHT. Any two should raise the question.
2
Diagnose appropriately
Three or more Curaçao Criteria is a definite diagnosis; two is possible or suspected. Genetic testing confirms when findings are equivocal and identifies at-risk relatives. ICD-10 code I78.0.
3
Screen beyond symptoms
Pulmonary AVMs occur in at least 40% of people with HHT and are often asymptomatic until a paradoxical embolic event. Screening is guideline-recommended regardless of symptoms.
4
Know when to refer
Suspected or confirmed HHT, a need for comprehensive screening, complex manifestations, or planning around pregnancy are all reasonable grounds for evaluation at a Center of Excellence.
5
Send the patient home with tools
The comprehensive patient guide, care checklists, and an emergency wallet card do work between appointments, particularly in emergency departments unfamiliar with HHT.
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Remember the family
HHT is autosomal dominant. Each first-degree relative has a 50% chance of being affected, which makes one diagnosis a screening opportunity for an entire family.
Common misconceptions
What the guidelines say that surprises people
HHT is a vascular malformation disorder, not a coagulopathy. Standard coagulation studies are typically normal, and a normal workup does not argue against the diagnosis.
Anticoagulant and antiplatelet therapy are not absolutely contraindicated. The guidelines support their use when medically indicated, with stated preferences among agents and a caution against combining antiplatelet and anticoagulant therapy unnecessarily.
Iron deficiency should be assessed in every adult with HHT regardless of symptoms, and in children with recurrent bleeding or symptoms of anemia.
Prevalence and burden
1 in 4,000
Estimated prevalence
80%
Remain undiagnosed
40%+
Have pulmonary AVMs, frequently asymptomatic
27 yrs
Average delay to diagnosis
Molecular genetics
The genes associated with HHT
HHT is inherited in an autosomal dominant pattern. Four genes are currently associated with the condition, and the genotype carries clinical weight: it shifts which manifestations are most likely and, in one case, adds a surveillance requirement that has nothing to do with bleeding.
| Gene | Share of cases | Clinical implication |
|---|---|---|
| ENG HHT type 1 | ENG and ACVRL1 together account for approximately 90% | Pulmonary AVMs are 5 to 10 times more likely than in HHT2. |
| ACVRL1 HHT type 2 | ENG and ACVRL1 together account for approximately 90% | Hepatic vascular malformations are more often symptomatic, and presentation tends to be later. |
| SMAD4 | 3% to 5% of clinically diagnosed individuals | Combined syndrome of HHT and juvenile polyposis. Gastrointestinal surveillance, including colonoscopy from adolescence, is part of management. |
| GDF2 (BMP9) | Fewer than 1% | Reported in only a handful of individuals worldwide and not typically included in routine HHT panels. |
| No variant identified | About 10% to 15% | A clinical diagnosis stands on its own. Additional causative genes are presumed but not yet identified. |
A negative genetic result does not exclude HHT. Because 10% to 15% of people with a clinical diagnosis carry no variant in a known HHT gene, testing is most useful for confirming equivocal cases and for cascade testing of at-risk relatives once a familial variant has been identified.