“Thrombocytopenia-absent radius (TAR) syndrome is a rare disorder that is present at birth (congenital). It is characterized by low levels of platelets in the blood (thrombocytopenia) and absence (aplasia) of the long, thin bones of the forearms (radii) but with presence of thumbs. Other abnormalities are often present including additional skeletal defects such as absence or underdevelopment of the other bone of the forearm (ulna), structural malformations of the heart (congenital heart defects) and kidney (renal) defects.”

NORD National Organization For Rare Diseases (https://rarediseases.org/rare-diseases/thrombocytopenia-absent-radius-syndrome/)