Thrombocytopenia with absent radius (TAR) syndrome is primarily characterized by the following two features:
- fetal thrombocytopenia
- absent fetal radii (bilaterally) with the presence of both thumbs
The condition is extremely rare with an estimated incidence of 0.4 per 100,000 births.
The principal defect is thought to absent or arrested development of the megakaryocyte progenitor cell or a progenitor cell with a maturational defect as there is minimally deleted region on chromosome 1q21.1 (deletion/duplication syndrome).
It is thought to carry an autosomal recessive inheritance with variable penetrance 3,8.
- cleft lip +/- palate
- congenital cardiac anomalies in ~30%
- jaw under development: micrognathia
- partial absence of lower limbs
- fibula aplasia: ~50% 8
Sonographic features include:
- bilateral absence of radii with normal thumbs 3 (crucial to the diagnosis)
- radial deviation of the hands
- the ulna is abnormal (usually shortened and malformed but may be absent bilaterally in ~20% of cases and unilaterally in ~10% of cases).
- the humerus is abnormal in almost 50% of cases and absent bilaterally (humeral aplasia) in 5-10% of cases (a five fingered hand arises from the shoulder)
- asymmetrical limb shortening, abnormalities of the shoulder joint and hypoplasia of the glenoid fossa, scapulae and clavicles and soft tissues of the arm and shoulder have been reported
- synostosis of the metacarpal bones
- hypoplastic digits
Treatment and prognosis
Although the TAR syndrome is not uniformly fatal, early prenatal diagnosis is important as the morbidity and mortality associated with this condition may be high. The prognosis is thought to be good if the patient survives to at least one year of age 6 where there is improvement of the thrombocytopenia.
Management options include intrauterine platelet transfusion to prevent fetal hemorrhage in labor; a planned atraumatic delivery (cesarean section) or termination of pregnancy in the second trimester may be contemplated.
- intracranial hemorrhage: especially during the 1st year of life can impair mental development
History and etymology
The TAR syndrome was initially described by H Gross et al. in 1956 4.
The following diseases show radial hypoplasia as a component manifestation:
- Holt-Oram syndrome
- Fanconi anemia
- Roberts syndrome
- thalidomide embryopathy
- VACTERL anomalies
- Duane anomaly
- Townes-Brocks syndrome
- RAPADILINO syndrome
- 1. Donnenfeld AE, Wiseman B, Lavi E et-al. Prenatal diagnosis of thrombocytopenia absent radius syndrome by ultrasound and cordocentesis. Prenat. Diagn. 1990;10 (1): 29-35. - Pubmed citation
- 2. Shelton SD, Paulyson K, Kay HH. Prenatal diagnosis of thrombocytopenia absent radius (TAR) syndrome and vaginal delivery. Prenat. Diagn. 1999;19 (1): 54-7. Prenat. Diagn. (link) - Pubmed citation
- 3. Boute O, Depret-mosser S, Vinatier D et-al. Prenatal diagnosis of thrombocytopenia-absent radius syndrome. Fetal. Diagn. Ther. 11 (3): 224-30. - Pubmed citation
- 4. Gross. H, Groh C, Weippl G. Congenitale hypoplastische thrombopenie mit radialaplasie. Neue Osterr Z Kinderheilkd 1956, 1:574.
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- 6. Hall JG, Levin J, Kuhn JP et-al. Thrombocytopenia with absent radius (TAR). Medicine (Baltimore). 1969;48 (6): 411-39. - Pubmed citation
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- 8. Entezami M, Albig M, Knoll U et-al. Ultrasound Diagnosis of Fetal Anomalies. Thieme. (2003) ISBN:1588902129. Read it at Google Books - Find it at Amazon
- 9. Semmekrot BA, Haraldsson A, Weemaes CM et-al. Absent thumb, immune disorder, and congenital anemia presenting with hydrops fetalis. Am. J. Med. Genet. 1992;42 (5): 736-40. doi:10.1002/ajmg.1320420523 - Pubmed citation
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