SNP Shot: Genomic Insights

Hereditary hemorrhagic telangiectasia (HHT) is a genetic condition characterized by the development of various blood vessel abnormalities.

Typically, the heart pumps oxygen-rich blood from the lungs, through arteries, at a high pressure. This pressure drives the blood into smaller vessels (arterioles and capillaries) which supply oxygen to the body's tissues. The blood pressure reduces considerably by the time it reaches the capillaries. From the capillaries, blood flows into veins and eventually returns to the heart.

In individuals with HHT, some arteries connect directly to veins, bypassing the capillary network. These abnormal connections are called arteriovenous malformations (AVMs). When these AVMs occur near the skin's surface, they appear as small, red marks called telangiectases (singular: telangiectasia).

Without the buffering effect of the capillaries, high-pressure blood from the arteries flows directly into the more fragile veins. This increased pressure weakens and enlarges the veins, potentially compressing or irritating adjacent tissues. This often leads to frequent and severe bleeding (hemorrhage). Nosebleeds are extremely common in those with HHT, and serious hemorrhages can occur in organs like the brain, liver, or lungs.

There are different types of HHT, primarily classified by their genetic cause, but also exhibiting some variations in symptoms. Individuals with type 1 often experience symptoms earlier and have a higher likelihood of developing AVMs in the lungs and brain compared to those with type 2. Types 2 and 3 may be associated with an increased risk of liver involvement. Women with type 1 are more prone to lung AVMs than men, and also have a higher risk of liver involvement with types 1 and 2. However, individuals with any type of HHT can experience any of these complications.

Juvenile polyposis/HHT syndrome combines AVMs with a predisposition to developing polyps (growths) in the gastrointestinal tract. HHT types 1, 2, and 3 do not seem to increase the risk of developing these polyps.

Inheritance:

HHT is inherited in an autosomal dominant pattern. This means that only one copy of the mutated gene in each cell is enough to cause the condition.