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In the mid 1990s, scientists discovered that an abnormal gene on either chromosome 9 or 12 causes HHT. Chromosome 9 (endoglin) and chromosome 12 (activin-like kinase) tell the body to produce a substance that is involved in the formation of blood vessels. HHT is a dominant disorder since one abnormal copy of the gene from one parent can cause the disorder. Although there is a 50 percent chance of inheriting this abnormal gene, children who do not have it cannot pass on the disease.
In 2003, genetic testing for HHT became available at only a few genetics laboratories in the United States. The complicated family-based testing should be run, ordered and managed by an HHT Center or genetics professional.
According to recently published Clinical Diagnostic Criteria, a person has HHT if they have three or more of the following criteria and are suspect if they have two or more of the criteria:
Nosebleeds are spontaneous and recurrent
Telangiectases are prevalent at characteristic sites such as lips, oral cavity, fingers and nose
AVMs are present in lung, brain, GI, liver or spine
Family history indicates a parent, sibling or child has HHT