Thrombocytopenia with Absent Radii (TAR) Syndrome Without Significant Thrombocytopenia

Thrombocytopenia with absent radii (TAR) syndrome is a rare genetic syndrome that occurs with a frequency of about 0.42 cases per 100,000 live births. It is characterized by hypo-megakaryocytic thrombocytopenia with bilateral absent radii and the presence of both thumbs. The thrombocytopenia is initially very severe, manifesting in the first few weeks to months of life, but subsequently improves with time to reach near normal values by one to two years of age. We present a case of a newborn with TAR syndrome with an atypical presentation of mild thrombocytopenia in the first week of life, with early normalization of platelet counts in the neonatal period. The patient deviates from the normal pattern in which 95% of patients with TAR syndrome usually develop significant thrombocytopenia (platelet counts of less than 50 x 10 ⁹ platelets/L) within the first four months of life. Additionally, the absence of hypo-megakaryocytes on peripheral smear sets this patient apart from the typical cases of TAR syndrome. TAR syndrome is often associated with significant morbidity and mortality secondary to severe thrombocytopenia, which occurs with the highest frequency in the first 14 months of life. The most common cause of mortality is due to a severe hemorrhagic event occurring in the brain, gastrointestinal tract, and other organs. Therefore, all patients with TAR syndrome should be monitored closely for symptomatic thrombocytopenia with platelet transfusions being implemented as the first-line therapy for the treatment of severe or symptomatic disease.