National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

TAR syndrome


Other Names:
Thrombocytopenia absent radius syndrome; Absent radii and thrombocytopenia; Thrombocytopenia absent radii
Categories:
TAR syndrome is characterized by the absence of a bone called the radius in each forearm, short stature, and thrombocytopenia. The thrombocytopenia often appears first in infancy but becomes less severe or returns to normal over time. Infants and young children are particularly vulnerable to episodes of severe bleeding which may occur in the brain and other organs. Children who survive this period and do not have damaging bleeding in the brain usually have a normal life expectancy and normal intellectual development. Other signs and symptoms vary but may include heart defects, kidney defects, and other skeletal abnormalities. About half of people with TAR syndrome also have difficulty digesting cow's milk. TAR syndrome is thought be caused by a deletion of genes on chromosome 1q21.1 in concert with another genetic change that has yet to be identified. Click here to see a diagram of chromosome 1.[1]
Last updated: 3/26/2012

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Abnormality of coagulation 0001928
Absent radius
Missing outer large bone of forearm
0003974
Aplasia/Hypoplasia of the ulna
Absence/underdevelopment of inner forearm bone
0006495
Thrombocytopenia
Low platelet count
0001873
30%-79% of people have these symptoms
Adducted thumb
Inward turned thumb
0001181
Anemia
Low number of red blood cells or hemoglobin
0001903
Aplasia/hypoplasia of the humerus
Absent/small long bone in upper arm
Absent/underdeveloped long bone in upper arm
[ more ] 		0006507
Aplasia/Hypoplasia of the patella
Absent/small kneecap
Absent/underdeveloped kneecap
[ more ] 		0006498
Broad forehead
Increased width of the forehead
Wide forehead
[ more ] 		0000337
Broad thumb
Wide/broad thumb
Broad thumbs
[ more ] 		0011304
Clinodactyly of the 5th finger
Permanent curving of the pinkie finger
0004209
Cow milk allergy
Milk allergy
0100327
Coxa valga 0002673
Eosinophilia
High blood eosinophil count
0001880
Genu varum
Outward bow-leggedness
Outward bowing at knees
[ more ] 		0002970
High forehead 0000348
Hip dislocation
Dislocated hips
Dislocation of hip
[ more ] 		0002827
Low-set, posteriorly rotated ears 0000368
Patellar aplasia
Absent kneecap
0006443
Patellar dislocation
Dislocated kneecap
0002999
Tibial torsion 0100694
5%-29% of people have these symptoms
Abnormal cardiac septum morphology 0001671
Abnormality of the shoulder 0003043
Aplasia of the uterus
Absent uterus
uterus absent
[ more ] 		0000151
Axial malrotation of the kidney 0004717
Carpal bone hypoplasia
Small carpal bones
Small carpals
[ more ] 		0001498
Cavum septum pellucidum 0002389
Cerebellar hypoplasia
Small cerebellum
Underdeveloped cerebellum
[ more ] 		0001321
Cervical ribs 0000891
Cleft palate
Cleft roof of mouth
0000175
Coarctation of aorta
Narrowing of aorta
Narrowing of the aorta
[ more ] 		0001680
Delayed CNS myelination 0002188
Edema of the dorsum of feet 0012098
Edema of the dorsum of hands 0007514
Fibular aplasia
Absent calf bone
0002990
Finger syndactyly 0006101
Fused cervical vertebrae
Fused neck
0002949
Global developmental delay 0001263
Hepatosplenomegaly
Enlarged liver and spleen
0001433
Horseshoe kidney
Horseshoe kidneys
0000085
Lateral clavicle hook
Hook-shaped collarbone
0000895
Malar flattening
Zygomatic flattening
0000272
Micrognathia
Little lower jaw
Small jaw
Small lower jaw
[ more ] 		0000347
Nevus flammeus of the forehead
Port-wine stain on forehead
0007413
Phocomelia 0009829
Ptosis
Drooping upper eyelid
0000508
Scoliosis 0002650
Sensorineural hearing impairment 0000407
Short phalanx of finger
Short finger bones
0009803
Strabismus
Cross-eyed
Squint
Squint eyes
[ more ] 		0000486
Talipes equinovarus
Club feet
Club foot
Clubfeet
Clubfoot
[ more ] 		0001762
Tetralogy of Fallot 0001636
1%-4% of people have these symptoms
Bilateral radial aplasia 0004977
Death in infancy
Infantile death
Lethal in infancy
[ more ] 		0001522
Short stature
Decreased body height
Small stature
[ more ] 		0004322
Ventricular septal defect
Hole in heart wall separating two lower heart chambers
0001629
Percent of people who have these symptoms is not available through HPO
Anteverted nares
Nasal tip, upturned
Upturned nasal tip
Upturned nose
Upturned nostrils
[ more ] 		0000463
Atrial septal defect
An opening in the wall separating the top two chambers of the heart
Hole in heart wall separating two upper heart chambers
[ more ] 		0001631
Autosomal recessive inheritance 0000007
Brachycephaly
Short and broad skull
0000248
Carpal synostosis 0009702
Decreased circulating antibody level 0004313
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific
Mental-retardation
[ more ] 		0001249
Meckel diverticulum 0002245
Motor delay 0001270
Pancreatic cysts 0001737
Seborrheic dermatitis 0001051
Seizure 0001250
Shoulder muscle hypoplasia
Underdeveloped shoulder muscle
0008952
Spina bifida 0002414
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Last updated: 7/1/2020

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.
  • Orphanet lists international laboratories offering diagnostic testing for this condition.

The resources below provide information about treatment options for this condition. If you have questions about which treatment is right for you, talk to your healthcare professional.

Management Guidelines

  • Project OrphanAnesthesia is a project whose aim is to create peer-reviewed, readily accessible guidelines for patients with rare diseases and for the anesthesiologists caring for them. The project is a collaborative effort of the German Society of Anesthesiology and Intensive Care, Orphanet, the European Society of Pediatric Anesthesia, anesthetists and rare disease experts with the aim to contribute to patient safety.
The first two years of life are the most critical in TAR syndrome.[2] During this time, children frequently develop life-threatening bleeding episodes due to extremely low platelet levels (thrombocytopenia). These episodes decrease with age, and platelet counts are usually normal by the time a child goes to school.[2] Many individuals with TAR syndrome are allergic to cow's milk, which can also exacerbate the symptoms of thrombocytopenia.[3] Intellectual development is usually not affected by TAR syndrome, though some individuals have intellectual disability due to complications from bleeding within the brain.[2] People with TAR syndrome may be at increased risk of developing acute leukemia during childhood or adulthood.[2]
Last updated: 2/19/2014

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources

Related diseases are conditions that have similar signs and symptoms. A health care provider may consider these conditions in the table below when making a diagnosis. Please note that the table may not include all the possible conditions related to this disease.

Conditions with similar signs and symptoms from Orphanet
The main differential diagnoses include Holt-Oram syndrome, Roberts syndrome, Fanconi anemia, thalidomide embryopathy and RAPADILINO syndrome (see these terms).
Visit the Orphanet disease page for more information.

Research helps us better understand diseases and can lead to advances in diagnosis and treatment. This section provides resources to help you learn about medical research and ways to get involved.

Patient Registry

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

Social Networking Websites

  • RareConnect is an online social network for patients and families to connect with one another and share their experience living with a rare disease. The project is a joint collaboration between EURORDIS (European Rare Disease Organisation) and NORD (National Organization for Rare Disorders). Click on the link above to view the community for limb differences.

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • The Children’s Hospital Boston has a information page on congenital limb defects. Click on the link above to view this information page.
  • Genetics Home Reference (GHR) contains information on TAR syndrome. This website is maintained by the National Library of Medicine.
  • The National Cancer Institute provides the most current information on cancer for patients, health professionals, and the general public.

In-Depth Information

  • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
  • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss TAR syndrome. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know. Submit a new question

  • Has TAR syndrome been associated with white cell abnormalities in the bone marrow? What about cancer? See answer


  1. Thrombocytopenia-absent radius syndrome. Genetics Home Reference. October 2012; http://ghr.nlm.nih.gov/condition=thrombocytopeniaabsentradiussyndrome.
  2. John K Wu. Thrombocytopenia-absent radius syndrome. Medscape Reference. April 16, 2012; http://reference.medscape.com/article/959262-overview.
  3. Toriello, HV. Thrombocytopenia absent radius syndrome. GeneReviews. June 28, 2012; http://www.ncbi.nlm.nih.gov/books/NBK23758/.