TAR Syndrome
TAR syndrome (thrombocytopenia with absent radius) is a rare genetic disorder that is characterized by the absence of the radius bone in the forearm and a dramatically reduced platelet count.
Causes of TAR Syndrome
TAR syndrome is inherited as an autosomal recessive genetic disorder and caused by two different types of mutations in the RBM8A gene.
Recessive genetic disorders occur when an individual inherits two copies of an abnormal gene for the same trait, one from each parent.
If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disorder but usually will not show symptoms.
However, reports have been published that describe an affected child born to an affected parent.
- The risk for two carrier parents to both pass the defective gene and have an affected child is theoretically 25% with each pregnancy, but because the RBM8A gene deletion associated with TAR syndrome is often not inherited, but occurs as a new mutation in about 25% of those affected, the risk for affected sibs is lower.
- The risk to have a child who is a carrier like the parents is 50% with each pregnancy.
- The chance for a child to receive normal genes from both parents is 25%.
- The risk is the same for males and females.
Symptoms of TAR Syndrome
Presents with symptoms of thrombocytopenia, or a lowered platelet count, leading to bruising and potentially life-threatening hemorrhage.
Absence of the radius bone in the forearm with preservation of the thumb.
Other common links between people with TAR syndrome include anemia, heart problems, kidney problems, knee joint problems, and frequently milk allergy.
Different cases with leukemia in patients with TAR are described in.
Diagnosis of TAR Syndrome
Cardiac evaluation may also be recommended to detect any heart abnormalities that may be associated with the disorder.
Such evaluation may include a thorough clinical examination, during which heart and lung sounds are assessed through use of a stethoscope, and specialized tests that enable physicians to evaluate the structure and function of the heart (e.g., x-ray studies, electrocardiography [EKG], echocardiography, cardiac catheterization).
Treatment of TAR Syndrome
Treatments range from platelet transfusions to surgery aimed at either centralizing the hand over the ulna to improve functionality of the hand or aimed at ’normalizing’ the appearance of the arm, which is much shorter and ‘clubbed’.
There is some controversy surrounding the role of surgery.
The infant mortality rate has been curbed by new technology, including platelet transfusions, which can even be performed in utero.
The critical period is the first and sometimes second year of life.
For most people with TAR, platelet counts improve as they grow out of childhood.