Thrombocytopenia-absent radius (TAR) Syndrome is the absence of the radius (Radial Club Hand) along with a platelet deficiency (thrombocytopenia). Thrombocytopenia prevents normal blood clotting. Affected individuals are at a heightened risk of severe bleeding in the brain and other organs.

TAR Syndrome is also associated with short stature and associated deformities in the lower extremities, including knee deformities. The thumbs are usually present but hypoplastic (underdeveloped).

TAR Syndrome is a rare disorder, affecting 1 in 100,000 live births. The syndrome is caused by mutations in the RBM8A gene. This gene codes for a protein that is involved in the production of other proteins. This results in the irregular development of certain tissues. TAR Syndrome is inherited in an autosomal recessive pattern, meaning both copies of the allele must be present to express the syndrome.