TAR syndrome

What is TAR Syndrome?

Thrombocytopenia-absent radius (TAR) syndrome is a rare genetic disorder characterized by a low number of platelets in the blood (thrombocytopenia), which can cause bleeding episodes. There is an absence or underdevelopment of the radius bone in the forearm. Other features of TAR syndrome may include skeletal abnormalities in the hands, arms, and legs, heart defects, and internal organs, amongst others. TAR syndrome is usually diagnosed during prenatal ultrasound checks or at birth based on the characteristic physical features and a blood test to count the number of platelets. The condition is inherited in an autosomal recessive manner, meaning a child must inherit two copies of the mutated gene (one from each parent) to develop TAR syndrome. Thus, parents with identified genetic TAR-specific variations will have a 25% chance that their child will have this syndrome. However, spontaneous mutations may also occur without any genetic inheritance by parents. Treatment may involve platelet transfusions to prevent bleeding (especially in the first years) and surgery to correct skeletal abnormalities.

Thrombocytopenia

Thrombocytopenia is a medical condition characterized by a lower-than-normal number of platelets in the blood. Platelets are small, colorless cell fragments that help blood clot and prevent bleeding. When the number of platelets in the blood is reduced, bleeding and bruising may occur more easily.

Treatment for thrombocytopenia depends on the underlying cause and severity of the condition. In some cases, no treatment may be needed, while in other cases, treatment may involve medications to increase platelet production or prevent the destruction of platelets or transfusions of platelets. In children with TAR syndrome, the thrombocytopenia often improves as the child ages. Every TAR-Syndrome child is different, and the degree of thrombocytopenia varies.

Low platelet levels at birth might also be a transient thrombocytopenia: a temporary and typically mild decrease in the number of platelets in a newborn’s blood shortly after delivery.

Absent Radius (Radial Aplasia)

Radial Aplasia, also known as radial dysplasia, radial longitudinal deficiency, or radial clubhand, is a medical condition in which the radius bone in the forearm is either absent or underdeveloped. This can result in a shortened or missing forearm, a deformity of the hand, and a limited range of motion in the affected arm. Radial aplasia is usually diagnosed prenatally, or at birth.

Radial aplasia can occur as an isolated abnormality or as part of a larger syndrome, such as Holt-Oram syndrome, Fanconi anemia, or TAR syndrome. The cause of radial aplasia is poorly understood, but genetic factors often play a role.

Treatment for radial aplasia depends on the condition’s severity and any other associated abnormalities. In some cases, no treatment may be needed, while in others, treatment may involve surgery to improve the function and appearance of the affected arm. Occupational therapy and physical therapy is also recommended to help improve strength and mobility in the affected arm.

See our section on Radial Aplasia