Thrombocytopenia-absent radius syndromes

Philippe Jeanty, MD, PhD Sandra R Silva, MD

Definition: Congenital disorder described by Gross in 1956[1] characterized by bilateral radial aplasia with normal thumbs and thrombocytopenia at a level < 100.000/mm3.

Synonyms: TAR syndrome, Megakaryocytopenia-absent radius, radial aplasia-thrombocytopenia syndrome.

Incidence: Uncommon.

Etiology: Autosomal recessive disorder.

Recurrence risk: The recurrence risk is 25%.

Diagnosis: The major finding is that of bilateral club hand due to the missing radii. In some cases the abnormal position of the hands has been detected in the first timester[2]. A fetal blood sampling is then performed to assess the level of platelet and the number of megakaryocytes[3],[4]. When cardiac and renal anomalies are present, oligohydramnios may develop during the second trimester, making the evaluation of the limbs more difficult. In such a case, both amnioinfusion and fetoscopy have been proposed[5].

Genetic anomalies: Not known. Radial ray aplasia may result from chromosomal, teratogenic, genetic, and multifactorial causes.

Differential diagnosis: The most common differential diagnoses include Trisomy 18 and Holt-Oram syndrome. Other differential diagnoses include other limb reduction abnormalities, in particular those that may present associated thrombocytopenia (Fanconi pancytopenia: usually have aplasia of the thumbs and chromosome fragility; Roberts-SC syndrome: usually present cleft lip and palate and premature separation of centromeric heterochromatin; Aase syndrome: usually present just mild forms of skeletal deformities).

Associated anomalies: The following anomalies may associate with thrombocytopenia absent radius in variable incidence: anemia, eosinophilia, and skeletal defects of upper and lower extremities such as ulnar, humeral, and femoral hypoplasia, congenital hip dislocation, toe syndactyly, talipes equinovarus and genu varum[7]. Cardiac (30% of the cases) and renal defects may be found. An increase susceptibility to infections is also observed.

Prognosis: 40% of the affected die during early infancy[8]. Hemorrhage and heart disease are the main causes of death. 7% have mental impairment. Motor developmental retardation is expected due to the skeletal defects. Hematological profile improves with age6.   The prognosis improves after the first year of age.

Management: Termination of pregnancy can be offered before viability. The infusion of platelet has been advocated before delivery to prevent hemorrhages during delivery[9]. Postnatally transplantation of allogeneic bone marrow from histocompatible sibling may correct persistently low platelet count[10].


[1] Gross. H, Groh C, Weippl G. Congenitale hypoplastische thrombopenie mit radialaplasie. Neue Osterr Z Kinderheilkd 1956, 1:574.

[2] Boute O, Depret-Mosser S, Vinatier D, Manouvrier S, Martin de Lassale E, Farriaux JP, Monnier JC Prenatal diagnosis of thrombocytopenia-absent radius syndrome. Fetal Diagn Ther 1996 May-Jun;11(3):224-30

[3] Ergur Ar, Yergok YZ, Ertekin A, Tayyar M, Yilmazturk A Prenatal diagnosis of an uncommon syndrome: thrombocytopenia absent radius (TAR). Zentralbl Gynakol 1998;120(2):75-8

[4] Donnenfeld AE, Wiseman B, Lavi E, Weiner S Prenatal diagnosis of thrombocytopenia absent radius syndrome by ultrasound and cordocentesis. Prenat Diagn 1990 Jan;10(1):29-35

[5] Filkins K, Russo J, Bilinki I, Diamond N, Searle B. Prenatal diagnosis of thrombocytopenia absent radius syndrome using ultrasound and fetoscopy. Prenat. Diagn.1984, 4: 139-142.

[6] Donnenfeld AE, Wiseman B, Lavi E, Weiner S. Prenatal diagnosis of  thrombocytopenia absent radius syndrome by ultrasound and cordocentesis. Prenat Diagn. 1990, 10:29-35.

[7] Hedberg VA, Lipton JM. Thrombocytopenia with absent radii. A review of 100 cases. Am J Pediatr. Hematol. Oncol. 1988, 10: 51-64.

[8] Jones KL. Radial aplasia-thrombocytopenia syndrome in Smith’s recognizable patterns of human malformation. W.B. Saunders Company – Philadelphia, 1998,322-323.

[9] Weinblatt M, Petrikovsky B, Bialer M, Kochen J, Harper R Prenatal evaluation and in utero platelet transfusion for thrombocytopenia absent radii syndrome. Prenat Diagn 1994 Sep;14(9):892-6

[10] Brochstein JA, Shank B, Kernan NA, Terwilliger JW, O"Reilly RJ Marrow transplantation for thrombocytopenia-absent radii syndrome. J Pediatr 1992 Oct;121(4):587-9

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