Thrombocytopenia-Absent Radius Syndrome

Also known as: TAR syndrome, absent radii and thrombocytopenia, thrombocytopenia absent radii.

What is thrombocytopenia-absent radius syndrome?

Thrombocytopenia-absent radius syndrome, or TAR syndrome, is a rare disorder present at birth that is characterized by the absence of a bone called the radius in both forearms, as well as thrombocytopenia (low platelet count) and short stature.

What causes TAR syndrome?

TAR syndrome is a genetic inherited disorder thought to be caused by a deletion of genes on chromosome 1 with probably other genetic abnormalities at present not identified.

What are the symptoms of thrombocytopenia-absent radius syndrome?

In infants and young children significant bleeding from low platelet counts frequently occurs into the brain and other organs (like the bowel). Later thrombocytopenic episodes become less frequent though may be precipitated by stress, infections and diet.

While other signs, symptoms and severity vary:

• lack of radii
• abnormality of blood clotting
• anemia (and sometimes too many white blood cells)
• broad forehead (and other facial abnormalities)
• difficulty digesting cow’s milk
• heart defects
• kidney defects
• other bone abnormalities (e.g. fingers/toes) are common.

What are TAR syndrome care options?

There is no cure for TAR syndrome. During the first year of life avoidance of anything which will make bleeding worse, preventing head trauma, and supportive care with platelet transfusions to prevent bleeding are common.

Later other medical and surgical procedures may improve quality of life.

Reviewed by: Jack Wolfsdorf, MD, FAAP

This page was last updated on: September 16, 2025 12:20 PM