Thrombocytopenia with Absent Radii (TAR) Syndrome Without Significant Thrombocytopenia

Abstract

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 hypomegakaryocytic 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 hypomegakaryocytes 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.

Thrombocytopenia With Absent Radii Syndrome With an Unusual Urological Pathology: A Case Report

“…The first substantial investigation of the syndrome, which provided the syndrome its name, was published in 1969 [2]. Since then, the incidence has been reported to be between 0.42 per 100,000 live births and 1:200,000-1:100,000 [3,4]. The diagnosis may be confirmed if a patient has a microdeletion on chromosome 1q21 resulting in a null allele of the RNA-binding motif protein 8A (RBM8A) gene and a hypomorphic allele of the other RBM8A gene due to a pathogenic variant single nucleotide polymorphism (SNP) [4].…”

“…Since then, the incidence has been reported to be between 0.42 per 100,000 live births and 1:200,000-1:100,000 [3,4]. The diagnosis may be confirmed if a patient has a microdeletion on chromosome 1q21 resulting in a null allele of the RNA-binding motif protein 8A (RBM8A) gene and a hypomorphic allele of the other RBM8A gene due to a pathogenic variant single nucleotide polymorphism (SNP) [4]. The syndrome is characterized by a bilateral absence of radii accompanied by the presence of both thumbs and hypomegakaryocytic thrombocytopenia (HMT) [5].…”

“…The syndrome is characterized by a bilateral absence of radii accompanied by the presence of both thumbs and hypomegakaryocytic thrombocytopenia (HMT) [5]. Upon diagnosis of TAR syndrome, the thrombocytopenia can be quite severe; approximately 95% of patients with the condition have a platelet count of <50,000/uL, normalizing over time in most patients [4]. Immediately after birth, approximately 50% of infants with TAR syndrome have symptomatic thrombocytopenia, and by four months of life, 90% will be symptomatic [6].…”

“…Immediately after birth, approximately 50% of infants with TAR syndrome have symptomatic thrombocytopenia, and by four months of life, 90% will be symptomatic [6]. TAR syndrome has also been found to increase the occurrence of anomalies within hematologic, cardiovascular [4], gastrointestinal, and skeletal systems [7]. Cardiovascular anomalies may include tetralogy of Fallot or atrial septal defects [4].…”

“…TAR syndrome has also been found to increase the occurrence of anomalies within hematologic, cardiovascular [4], gastrointestinal, and skeletal systems [7]. Cardiovascular anomalies may include tetralogy of Fallot or atrial septal defects [4]. Skeletal anomalies may result in a higher risk of dental and craniofacial trauma in this patient population [7].…”