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Radial Aplasia-thrombocytopenia Syndrome

Radial aplasia-thrombocytopenia syndrome is a rare genetic disorder. It is also known as thrombocytopenia with absent radius, or TAR, syndrome. It was first described by Judith G. Hall, M.D., in 1969. Though researcher John K. Wu, M.D., has documented more than 20 symptoms of the disorder, its primary symptoms are a very low platelet count that leads to easy bruising and hemorrhaging, as well as the absence of the radius bone of the forearm. It occurs approximately 4.2 times in every 1 million live births. Though TAR syndrome can cause early death due to hemorraging or organ defects, children who have it and receive effective treatment may be able to have normal life spans and live independently.

  1. Primary Symptoms

    • The symptoms of TAR syndrome include primary symptoms, ones that are caused directly by the genetic anomaly, and secondary symptoms, caused by the primary symptoms. Not all people with TAR syndrome have all of the primary or secondary symptoms, but all patients are missing the radius in one or both arms and show thrombocytopenia, or very low platelet count, symptoms within the first 18 months of life.

      Primary symptoms:
      Thrombocytopenia--very low numbers of platelets, cell fragments that are necessary for blood clotting
      Underdeveloped or absent megakaryocytes, bone marrow cells that produce platelets
      Eosinophilia--high numbers of eosinophils, blood cells that combat infection
      Anemia--low blood iron
      Missing radius bone in one or both arms
      Missing, abnormal or underdeveloped ulna bone in one or both arms
      Abnormal shoulder joints
      Dislocated hips
      Knees and/or kneecaps are partially dislocated or abnormally grown together
      Femoral torsion--long bone of the thigh twisted out of position
      Tibial torson--shinbone is twisted
      Absence of fibula (calf bone)
      Small feet with abnormal toe placement
      Severe intolerance to cow's milk
      Heart defects
      Kidney defects
      Underdeveloped uterus and vagina

    Secondary symptoms

    • Bruising and/or hemorrhaging due to thrombocytopenia
      Early death due to hemorrhaging
      Wrist and knee arthritis due to eosinophilia and dislocations
      Intestinal bleeding due to milk intolerance
      Infertility in women due to uterine deformities

    Prognosis

    • Children born with TAR syndrome are likely to have chronic thrombocytopenia, plus times when their thrombocytopenia becomes more acute and causes severe bruising and hemorrhaging. However, by age 6, most children with the condition develop near-normal platelet counts, and the risk of hemorrhaging becomes minor. According to Wu, if a child with the condition lives past age 2, she will have a normal life expectancy.

      People who have radial aplasia--missing radius bone or bones--and no other arm deformities can learn to perform all normal activities of daily living if they receive appropriate orthotic arm bracing. The prognosis for people who have organ defects and skeletal defects beyond the arms depends on the type of defect and the treatment they receive.

    Treatment

    • Treatment will depend on the type and severity of symptoms. Wu states, "By far, the most important treatment is platelet transfusion." Other common treatments include use of custom orthotic bracing and surgeries to make the affected limbs more functional, symmetrical or cosmetically appealing. Though amputation to prepare the patient to wear a prosthetic limb or limbs is an option, people with radial aplasia-thrombocytopenia syndrome oftentimes don't have enough core-muscle strength to use a prosthesis effectively, and patients with functional hands generally find them more useful than the longer arms that prostheses provide.
      Bone marrow transplantation is an option for people whose tendency to hemorrhage doesn't improved with platelet transfusions.
      Intestinal problems due to cow's milk intolerance can be dealt with by removing cow's milk from the diet.

    Preventing Problems

    • Patients and their families can prevent many of the hemorrhaging episodes associated with TAR syndrome. Good preventive measures include the following:
      Undergoing platelet transfusions
      Avoiding injuries--wearing a soft helmet can help
      Avoiding use of drugs that decrease clotting, including aspirin and nonsteroidal anti-inflammatory drugs, or NSAIDs
      Treating minor cuts and injection sites by placing prolonged, firm, steady pressure on them until they stop bleeding

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