Thrombocytopenia absent radius (TAR) syndrome is a rare disorder that is congenital (present at birth). Thrombocytopenia is a general term for blood disorders that cause low levels of platelets. A platelet is a type of blood cell that helps the blood clot. These cells clump together at the site of a blood vessel injury in order to prevent blood loss. Therefore, thrombocytopenia is often associated with abnormal bleeding. TAR syndrome is characterized by very low levels of platelet-producing cells, called hypomegakaryocytic thrombocytopenia, associated with bilateral radial aplasia. This means that in addition to having dramatically low platelet levels, the bone that connects the elbow to the thumb side of the wrist (called the radius) fails to grow in both arms.
TAR syndrome was first defined as a syndrome in 1969. TAR can have varied symptoms, which can include abnormalities in the digestive, bone, blood, and heart systems. Despite the absence of the radius bones, TAR patients usually have both of their thumbs, although thumb function is very limited.
Bone defects are often present in individuals affected with TAR. In addition, TAR patients may be short for their age and are commonly intolerant of cow's milk.
Although TAR syndrome is not completely understood, it is generally believed to be inherited because it has affected more than one member of some families. However, further research is needed to confirm this genetic link. Evidence has suggested that TAR syndrome may be the result of a more complex inheritance pattern; other theories also exist.
The symptoms and complications of TAR syndrome are the most severe during infancy and almost all deaths occur before age two. Those that survive beyond age two may have normal life expectancies. There are a number of adults living with TAR syndrome, which suggests that there are few additional problems that develop during adulthood. Most adults with TAR syndrome are able to live independently and have productive jobs despite physical limitations from the disease. In addition, the Internet has become a valuable means of connection between people with TAR, who often feel isolated because the condition is so rare.
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