Thrombocytopenia Absent Radii (TAR)

What is Thrombocytopenia Absent Radii (TAR)?

Thrombocytopenia-absent radius (TAR) syndrome is a rare condition with two main findings. Children with TAR have decreased production of platelets (the cells which help the blood to clot) and are missing one of the two bones from each lower arm, called the radius.

What are the signs and symptoms of TAR?

Children with TAR are almost always diagnosed at birth. Signs and symptoms include the following:

  • Bruising and bleeding as a result of the decreased platelets
  • Missing radius bone from both lower arms (although the thumbs are present)
  • Short stature and additional skeletal abnormalities, including underdevelopment of other bones in the arms and legs
  • Malformations of the heart and kidneys
  • Associated features may also include a small lower jaw (micrognathia), a prominent forehead, and low-set ears
  • About half of affected individuals experience difficulty digesting cow's milk

How is TAR diagnosed?

The diagnosis is made by physical examination, in which the radius bones in the arms are found to be missing. Blood tests are done to assess the platelet count and for genetic analysis of chromosome 1. Affected individuals have a deletion (absence) of chromosome 1 at position 1q21.1.

How is TAR treated?

The critical period is the first year of life. Platelet transfusions are required to prevent life threatening bleeding. For most children with TAR, platelet counts improve as they grow out of childhood. Surgery may also be required for skeletal abnormalities.

About treatment for Thrombocytopenia Absent Radii at Children’s
Children’s Cancer and Blood Disorders program achieves outcomes that rank among the top national programs and cares for more than two-thirds of Minnesota children and adolescents with blood disorders. In the program, families coping with anemia have access to the newest and most promising treatments and receive care spearheaded and coordinated by a board-certified hematologist/oncologist.

Contact us
If you are a family member looking for a Children’s hematologist or oncologist or wanting to schedule an appointment, call the outpatient clinic at Children’s – Minneapolis at (612) 813-5940

If you are a health professional looking for consultation or referral information, please call Children's Physician Access at 1-866-755-2121 (toll-free).