TAR syndrome

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

Epidemiology

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

Pathology

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).

Genetics

It is thought to carry an autosomal recessive inheritance with variable penetrance .

Associations

Radiographic features

Antenatal ultrasound

Sonographic features include:

  • bilateral absence of radii with normal thumbs (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 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.

Complications

History and etymology

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

Differential diagnosis

The following diseases show radial hypoplasia as a component manifestation:

See also

Siehe auch:
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