Details
Condition Overview
TAR Syndrome is a rare condition that affects the arms and the blood.
People with TAR Syndrome are usually born without the radius bone in both forearms. The radius is the bone on the thumb side of the arm. One feature that helps distinguish TAR Syndrome from similar conditions is that people with TAR Syndrome usually have thumbs.
TAR Syndrome also causes low platelet levels, especially during infancy. Platelets help the blood clot and stop bleeding. When platelet levels are low, a baby may bruise easily, have frequent nosebleeds, or experience more serious bleeding. The risk of severe bleeding is usually highest during the first year of life, so close medical care and platelet monitoring are especially important during this time.
For many people, platelet levels improve as they get older and may eventually return to a normal range. Children who do not experience serious bleeding in the brain usually have typical intellectual development and a normal life expectancy.
TAR Syndrome can affect each person differently. Some people may also have differences in the other bones of the arms, hands, legs, hips, heart, or kidneys. These differences can range from mild to more complex.
Some babies and children with TAR Syndrome also react to cow’s milk. In certain cases, this reaction may cause platelet levels to drop further. Families should discuss feeding concerns and possible milk sensitivity with their child’s medical team.
Although a TAR Syndrome diagnosis can feel overwhelming, many individuals grow up to live active, meaningful, and fulfilling lives. The right medical care, information, tools, and community support can help families navigate each stage of the journey.
Long Arm TAR
- This term usually describes the classic and most common presentation. The infant is missing only the radius (the forearm bone on the thumb side). Crucially, affected individuals always have fully formed thumbs. The hands may angle inward (radial club hand) but fingers are generally present.
Short Arm TAR
- This refers to a more severe limb difference where the infant is missing all three primary bones in the arm (the radius, ulna, and sometimes the humerus). In these cases, the hands are typically attached much closer to the shoulders.
Lower Limb Variations
- About half of all individuals with TAR also experience some degree of leg skeletal abnormalities, ranging from mild hip or knee deformities to partial absence of the lower limbs
Core Symptoms & Features
- Hematologic Issues: Low platelet levels (thrombocytopenia) lead to easy bruising and a risk of severe, life-threatening hemorrhages—especially during the first year of life.
- Dietary Intolerance: About half of all TAR patients have a severe, sometimes worsening allergic reaction to cow's milk, which can impact their platelet counts.
- Organ Malformations: Some individuals may have congenital heart defects (such as atrial septal defects or tetralogy of Fallot) or kidney anomalies.
- Facial Features: Distinctive facial characteristics can include a small lower jaw, prominent forehead, and low-set ears.
- Missing Ligaments: Some individuals experience missing or malformed ligaments in areas such as the hands or knees.