Thrombocytopenia Absent Radius Syndrome

Thrombocytopenia-absent radius syndrome is a rare congenital disorder with seemingly unrelated abnormalities. This syndrome involves low levels of blood platelets (thrombocytopenia) and the absence of the radius bones in the forearms. Many other physical defects can occur in thrombocytopenia-absent radius syndrome, but the low platelet count holds the highest risk for life-threatening complications.

Prevalence

• According to the U.S. National Institutes of Health (NIH), thrombocytopenia-absent radius syndrome affects fewer than 1 in 100,000 babies. No ethnic, racial or gender differences in prevalence have been discovered. About half of the infants show symptoms in the first week after birth and 90 percent by 4 months of age, according to a study published in a 2007 issue of the Internet Journal of Radiology.

Thrombocytopenia

• Thrombocytopenia prevents normal blood clotting, leading to easy bruising and abnormal bleeding episodes. Severe internal bleeding may occur in the brain and other organs, particularly during the infant's first year. The condition gradually becomes less severe, and normal platelet counts usually are achieved by school age. If the child survives his first two years, life expectancy is normal, according to the Internet Journal of Radiology. Intellectual development also usually is normal, unless mental retardation has been caused by brain hemorrhaging.

Other Abnormalities

• The other definitive symptom of thrombocytopenia-absent radius syndrome is the absence of the long thin bone on the thumb side of the forearm. Additional abnormalities also can be present. These include underdevelopment or absence of the bone on the other side of the forearm (ulna), underdevelopment of other bones in the arms and legs, and short stature throughout life. The child also may have a small lower jaw, a prominent forehead and low-set ears. There may be heart and kidney structure defects. The NIH notes that about half these patients have difficulty digesting cow's milk.

Cause

• Thrombocytopenia-absent radius syndrome is a chromosomal disorder. The condition runs in families, but some people have the abnormality with no family history of the disorder. Additionally, some people with the abnormality do not have the syndrome as defined by chromosomal analysis. The NIH notes that because of these conflicting findings, researchers believe an additional genetic abnormality is involved.

Treatment

• Primary treatment involves preventing hemorrhaging episodes during the first year of life and rapidly resolving any that do occur. Frequent platelet transfusions may be provided to maintain sufficient platelet counts. Babies with kidney problems may benefit from dialysis. The baby also may benefit from splinting of the hands to improve function. Once the child has stable platelet counts, surgery may be able to correct arm deformities.