Overview
Osler-Weber-Rendu Syndrome, also known as Hereditary Hemorrhagic Telangiectasia (HHT), is a rare genetic disorder affecting the formation of blood vessels. It causes abnormal connections between arteries and veins (arteriovenous malformations, or AVMs) and small dilated blood vessels called telangiectasias. These abnormalities can occur in various organs, including the lungs, brain, liver, and gastrointestinal tract.
Who It Affects
HHT is an autosomal dominant genetic condition, meaning a child has a 50% chance of inheriting the condition if one parent carries the mutated gene. It affects both males and females equally and can manifest at any age, though symptoms often appear in childhood or young adulthood.
Prevalence
According to the Rare Disease Foundation, HHT affects approximately 1 in 5,000 people worldwide. However, many cases go undiagnosed because symptoms can be mild or develop slowly.
Symptoms
Symptoms of HHT can vary widely among individuals due to the unpredictable nature of AVMs and telangiectasias. Below is a list of common symptoms:
Nosebleeds (Epistaxis)
Frequent or severe nosebleeds are often the first sign of HHT. These occur due to telangiectasias in the nasal mucosa.
Telangiectasias
Visible small red or purple spots on the skin, lips, tongue, or inside the mouth and nose. These are dilated blood vessels that may bleed easily.
Arteriovenous Malformations (AVMs)
Hidden AVMs in organs like the lungs, brain, or liver can cause complications. Symptoms depend on the location:
Pulmonary AVMs
Can lead to hemoptysis (coughing up blood) or high-altitude pulmonary edema (HAPE).
Brain AVMs
May cause stroke, seizures, or brain abscesses.
Liver AVMs
Can result in abscesses or gastrointestinal bleeding.
Chronic Anemia
Repeated bleeding can lead to iron deficiency or anemia, causing fatigue, pallor, or shortness of breath.
Causes and Risk Factors
HHT is caused by mutations in specific genes responsible for blood vessel development. The primary genes involved are:
Endoglin (ENG)
Mutations here are the most common cause (about 50% of cases), according to the NIH.
ALK1 (ACVRL1)
Responsible for 15-20% of cases.
ALK2 or MERRF (MERL2)
Accounts for 10-15% of cases.
Risk Factors
The primary risk factor is a family history of HHT. Other factors include:
- Ethnic background: HHT is more commonly diagnosed in individuals of European descent.
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