TAR Syndrome

TAR is an acronym that stands for Thrombocytopenia, Absent Radius. This is a rare condition that is most severe in the neonatal period and early infancy and which is associated with thrombocytopenia and bilateral radial aplasia. It was first described in 1951. An autosomal recessive inheritance disorder that presents with abnormalities in skeletal, gastrointestinal, hematologic, and cardiac systems. Pancytopenia similar to Fanconi. The major cause of mortality is hemorrhage. The incidence of hemorrhage is limited to the first 14 months of life.

The frequency is 0.42 cases per 100,000 live births in Spain. Male:female ratio is equal. This medical condition is very rare in the United States.

Autosomal recessive.

Unknown. It is suggested that the “TAR gene” probably exerts its effect between gestation weeks 4 and 8 because this would explain the association of limb deformity and congenital heart disease found in this syndrome.

Finding of bilateral absence of the radius and thrombocytopenia.

Skeletal anomalies in addition to absent radii include ulnar hypoplasia, humeral hypoplasia, shoulder girdle hypoplasia, various hand anomalies, and lower limb dysplasias. Mandibular and maxillary hypoplasia are occasional findings. Congenital cardiac disease occurs in 30% of patients, most commonly tetralogy of Fallot and atrial septal defect. Additional findings may include hepatosplenomegaly and renal abnormalities. Symptomatic thrombocytopenia occurs in 50% of patients by the age of 1 week, although it may not occur until early adult life. Purpura, petechiae, epistaxis, gastrointestinal hemorrhage, and hematuria are common modes of presentation. Patients presenting outside the neonatal period may give a history of easy bruising. Thrombocytopenia may be episodic and is commonly precipitated by infection. In those patients surviving to adult life, the thrombocytopenia tends to be less severe and may be asymptomatic. Laboratory investigations may reveal a normal or low platelet count and eosinophilia. During episodes of thrombocytopenia, a leukocytosis with left shift is common. Anemia is usually secondary to blood loss rather than marrow aplasia. Megakaryocytes are not seen on examination of the bone marrow. The thrombocytopenia has been treated by steroids and splenectomy.

Careful assessment of airway for maxillary/mandibular hypoplasia. Cardiovascular assessment: examine for evidence of cardiac disease; consider ECG and echocardiography. Cardiac catheterization as indicated by proposed procedure and cardiac status. Laboratory investigations: full blood cell count, electrolytes, urea, and creatinine. Correct anemia secondary to blood loss; administer platelets preoperatively in presence of ongoing hemorrhage or if the platelet count is less than 50,000/mm3.

Presence of cardiac disease may dictate specific technique, risk of paradoxical air embolism should be considered in all these patients. Intravenous access may be difficult because of limb malformation, and central venous cannulation may be difficult because of shoulder girdle hypoplasia. The radial artery is usually present but may be abnormally positioned if intraarterial pressure monitoring is indicated. Ensure platelets are available for the perioperative period. Regional anesthesia is relatively contraindicated even in the absence of cardiac disease.

Nonsteroidal antiinflammatory drugs are contraindicated. Antibioprophylaxis in case of cardiac defect.