TAR syndrome

TAR syndrome, short for thrombocytopenia with absent radius, is a rare genetic disorder defined by two findings that occur together: the radius bone of the forearm is missing, usually with the thumb preserved, and the blood carries far fewer platelets than normal. The low platelet count leads to bruising, petechiae and, in the worst cases, life-threatening bleeding. Heart defects, kidney and knee joint problems, anemia, milk allergy and unusual facial features are also described. The condition needs changes in both copies of the relevant region, a deletion at 1q21.1 on one chromosome and a variant of the RBM8A gene on the other. Treatment ranges from platelet transfusions, which can even be given before birth, to hand surgery, and the first year or two of life is the critical period, after which platelet counts often improve. Greenwald and Sherman described the first patient in 1929, and the name was introduced decades later.