PP-07 TAR Syndrome case report

Objective

“Thrombocytopenia - absent radii Syndrome” (TAR) is characterized by hypo-megakaryocytic thrombocytopenia and bilateral absence of the radius bones despite the presence of both thumbs. It is rare and follows an autosomal recessive inheritance pattern. In individuals with TAR syndrome, skeletal, cardiac, gastrointestinal, hematological, renal, and genital abnormalities can also accompany the condition. Skeletal anomalies include varying degrees of ulnar hypoplasia, as well as hypoplasia of phalanges and carpal bones. Thumbs are always present. Thrombocytopenia improves with age and usually resolves by school age. It is associated with a deletion in the proximal region of the gene locus 1q21.1. The syndrome, first described in 1929, has an estimated prevalence of 0.42/100,000. In this case presentation, we aim to discuss the diagnosis and management of TAR syndrome.

Case

A 28-year-old woman, gravida 4, parity 1, abortion 1, was placed under routine pregnancy surveillance. During first-trimester screening, the absence of bilateral forearm segments and an increased nuchal translucency (3.8mm) were detected, prompting further monitoring. Amniocentesis was performed for the patient. In the second trimester, an obstetric ultrasound revealed the absence of the right forearm during upper extremity examination. Only a single bone consistent with the ulna was observed on the left side. Throughout the ultrasound examination, limited hand movement, significant wrist extension, and flexion contractures at the knees were noted. Additionally, there was pes equinovarus observed on the left foot. Differential diagnoses considered TAR syndrome, Roberts syndrome, and Fanconi syndrome. The amniocentesis yielded a normal fetal karyotype. At 40+1 weeks gestation by last menstrual period, the patient underwent a normal vaginal delivery with a birth weight of 3070g (19th percentile) and an 8-9 APGAR score. In the postnatal period, the infant was admitted to the neonatal intensive care unit due to a platelet count of 12000 and the presence of petechiae on the body. Absence of ulna and radius was observed on the right arm, while only a single bone consistent with ulna was seen on the left side. Postnatal microarray analysis was consistent with TAR syndrome.

Conclusion

TAR syndrome is an exceedingly rare condition. Prenatal diagnosis can be achieved through ultrasound evaluation of limb anomalies at around 16 weeks of gestation, combined with complete blood count and genetic analysis via cordocentesis. In neonates, when encountering thrombocytopenia and hemolytic anemia, TAR syndrome should be considered as a differential diagnosis. 

Keywords

TAR syndrome, absent radius, thrombocytopenia, hemolytic anemia, phocomelia

1. Hall, J. G. Thrombocytopenia and absent radius (TAR) syndrome. Journal of medical genetics. 24, 1987
2. Bozkurt Turhan, A., Barsan Kaya, T., Tekin, A. N., Anıl, H., Özdemir, C., & Akşit, M. A. Trombositopeni-Radius Yokluğu Sendromlu Yenidoğanda Hemolitik Anemi ve İnek Sütü İntoleransı Birlikteliği. Journal of Pediatric Disease/Cocuk Hastaliklari Dergisi. 2017

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