Thrombocytopenia with absent radius syndrome

Last revised by Mostafa El-Feky on 25 Aug 2022

Thrombocytopenia with absent radius (TAR) syndrome is primarily characterized by the following two features:

The condition is extremely rare with an estimated incidence of 0.4 per 100,000 births.

The principal defect is thought to be 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.

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

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 when there is an 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.

The TAR syndrome was initially described by H Gross et al. in 1956 4.

The following diseases show radial hypoplasia as a component manifestation:

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Cases and figures

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