Information about Hereditary Hemorrhagic Telangiectasia

Classification & external resources

ICD-10	I78.0
ICD-9	448.0
OMIM	187300
DiseasesDB	9303
eMedicine	med/2764  ped/1668 derm/782
MeSH	D013683

In medicine, hereditary hemorrhagic telangiectasia (HHT), also known as Osler-Weber-Rendu syndrome,^[1] is an autosomal dominant genetic disorder that leads to vascular malformations.

Signs and symptoms

HHT is characterised by telangiectasia (small vascular malformations) on the skin and mucosal linings, epistaxis (nosebleeds), and arteriovenous malformations (AVMs) in various internal organs. Skin and mucosa telangiectasias are most remarkable on the tongue, hands/fingers, nose, lips, mouth/throat and conjunctiva.

The internal organs that can harbor AVMs often include the brain and lungs. In both, bleeding can seriously endanger life. Anemia may occur due to bleeding from digestive tract AVMs. Congestive cardiac failure (high-output heart failure) may develop in the presence of marked shunting arterial blood to the venous circulation, e.g. when AVMs are present in the liver.

Diagnosis

There are four diagnostic criteria.^[2] If three or four are met, a patient has definite HHT, while two gives a possible diagnosis:

1. Spontaneous recurrent epistaxis
2. Multiple teleangiectasias on typical locations (see above)
3. Proven visceral AVM (lung, liver, brain, spine)
4. First-degree family member with HHT

When HHT is suspected, physical examination focuses on inspecting the whole skin for teleangiectasias, auscultation of the lungs and liver, and neurological examination.

Pulmonary AVMs can be anticipated by measuring oxygen levels and performing arterial blood gas (ABG) sampling. An X-ray of the chest can show susceptible lesions; in addition, low oxygen tension (<96% or a 2% decrease upon standing) or low blood oxygen levels on ABG are required for a diagnosis.

Genetics

HHT is a genetic disorder by definition. It is inherited in an autosomal dominant manner.

Four forms have been described:

• HHT1: mutation of the endoglin gene (ninth chromosome). Endoglin is a receptor of TGFβ1 (transforming growth factor beta 1) and TGFβ3. It also interacts with zyxin and ZRP-1 with its intracellular domain, to control composition of focal adhesions and regulate organization of actin filaments. This form predisposes for pulmonary AVMs and early nosebleeds.
• HHT2: mutation in the alk1 gene (12th chromosome). Alk-1 (activin receptor-like kinase 1) is a TGFβ1 receptor. Less pulmonary AVMs and later nosebleeds, but an increased risk of pulmonary hypertension (supposedly due to altered TGFβ signalling or other related pathways which may lead to vascular malformations).
• HHT3: a third form has been suspected to exist, but has not yet been linked to a defective gene. Current research is focused upon chromosome 5.^[3]
• Juvenile polyposis/hereditary hemorrhagic telangiectasia syndrome is caused by mutations in the gene SMAD4
• HHT4 has been identified in September 2006. The search for the gene associated with HHT4 is ongoing, with current research focused upon chromosome 7. ^[4]

It is possible to test patients for the presence of mutations in endoglin, ALK-1 and SMAD4. When the mutation in an affected family member has been found it is possible to test other family members and identify those people not at risk for developing the disease.

Pathophysiology

The mechanism underlying the formation of vascular malformations is not completely understood, but signalling of transforming growth factor-β1 is most likely to be involved. Possibly, connective tissue is required to support and guide proliferating blood vessels during angiogenesis, and defects in TGF-β signalling adversely affect connective tissue and matrix production.

Treatment

There is no specific treatment for the condition. Anemia due to bleeding from digestive tract AVMs often necessitates repeated blood transfusions. AVMs in critical organs often necessitates surgery.If major AVMs are all the patient has in terms of long-term problems, the surgery performed will block the malformed arteries, ruling out the risk for stroke and blood-clots. This surgery will hopefully lead to a normal life for the patient, and also help doctors diagnose patients with HHT more easily around the globe.

Epidemiology

HHT occurs mainly in whites (1:5,000), more in certain areas of France, but much less in blacks (1 in million). It is found in all continents throughout the world. It is also seen with increased frequency in Mormon families from Utah.

References

• Guttmacher AE, Marchuk DA, White RI Jr. Hereditary hemorrhagic telangiectasia. N Engl J Med 1995;333:918-24. PMID 7666879.

External links

• Mendelian Inheritance in Man (OMIM) 187300 (HHT1), Mendelian Inheritance in Man (OMIM) 600376 (HHT2), Mendelian Inheritance in Man (OMIM) 601101 (HHT3)
• HHT.org
• Information about Hereditary Hemorrhagic Telangiectasia from Children's Hospital, Seattle.

•  • [ e] Circulatory system pathology (, )
Hypertension	Hypertensive heart disease - Hypertensive nephropathy - Secondary hypertension (Renovascular hypertension)
Ischaemic heart disease	Angina pectoris - Prinzmetal's angina - Myocardial infarction - Dressler's syndrome
Pulmonary circulation	Pulmonary embolism - Cor pulmonale
Pericardium	Pericarditis - Pericardial effusion - Cardiac tamponade
Endocardium/heart valves	Endocarditis - Mitral regurgitation - Mitral valve prolapse - Mitral stenosis - Aortic valve stenosis - Aortic insufficiency - Pulmonary valve stenosis
Myocardium	Myocarditis - Cardiomyopathy (Dilated cardiomyopathy, Hypertrophic cardiomyopathy, Loeffler endocarditis, Restrictive cardiomyopathy) - Arrhythmogenic right ventricular dysplasia
Electrical conduction system of the heart	Heart block: AV block (First degree, Second degree, Third degree) - Bundle branch block (Left, Right) - Bifascicular block - Trifascicular block Pre-excitation syndrome (Wolff-Parkinson-White, Lown-Ganong-Levine) - Long QT syndrome - Adams-Stokes syndrome - Cardiac arrest Arrhythmia: Paroxysmal tachycardia (Supraventricular, AV nodal reentrant, Ventricular) - Atrial flutter - Atrial fibrillation - Ventricular fibrillation - Premature contraction (Atrial, Ventricular) - Sick sinus syndrome
Other heart conditions	Heart failure - Cardiomegaly - Ventricular hypertrophy (Left, Right)
Cerebrovascular diseases	Intracranial hemorrhage/cerebral hemorrhage: Extra-axial hemorrhage (Epidural hemorrhage, Subdural hemorrhage, Subarachnoid hemorrhage) - Intra-axial hematoma (Intraventricular hemorrhages, Intraparenchymal hemorrhage) - Anterior spinal artery syndrome - Binswanger's disease - Moyamoya disease
Arteries, arterioles and capillaries	Atherosclerosis (Renal artery stenosis) - Aortic dissection/Aortic aneurysm (Abdominal aortic aneurysm) - Aneurysm - Raynaud's phenomenon/Raynaud's disease - Buerger's disease - Arteritis (Aortitis) - Intermittent claudication - Arteriovenous fistula - Hereditary hemorrhagic telangiectasia - Spider angioma
Veins, lymphatic vessels and lymph nodes	Thrombosis/Phlebitis/Thrombophlebitis (Deep vein thrombosis, May-Thurner syndrome, Portal vein thrombosis, Venous thrombosis, Budd-Chiari syndrome, Renal vein thrombosis, Paget-Schroetter disease) - Varicose veins (Hemorrhoid, Esophageal varices, Varicocele, Gastric varices, Caput medusae) - Superior vena cava syndrome - Lymph(Lymphadenitis, Lymphedema, Lymphangitis)
See also (, )