TAR syndrome (

thrombocytopenia Thrombocytopenia is a condition characterized by abnormally low levels of platelets, also known as thrombocytes, in the blood. It is the most common coagulation disorder among intensive care patients and is seen in a fifth of medical patients a ...

with absent radius) is a rare

genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders ...

that is characterized by the absence of the

radius bone The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is usually slightly longer tha ...

in the forearm and a dramatically reduced

platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby i ...

count.

Signs and symptoms

* Presents with symptoms of

, or a lowered platelet count, leading to

bruising A bruise, also known as a contusion, is a type of hematoma of tissue, the most common cause being capillaries damaged by trauma, causing localized bleeding that extravasates into the surrounding interstitial tissues. Most bruises occur clos ...

and potentially life-threatening

hemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, v ...

. * Absence of the radius bone in the forearm with preservation of the thumb. Other common links between people with TAR syndrome include

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...

heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

problems,

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

problems, knee joint problems, and frequently

milk allergy Milk allergy is an adverse immune reaction to one or more proteins in cow's milk. Among the possible symptoms is anaphylaxis, a potentially life-threatening condition that requires treatment with Epinephrine (medication), epinephrine, among o ...

. Different cases with

leukemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ...

in patients with TAR are described in.

Genetics

This condition requires mutations in both chromosomes.Brodie SA, Rodriguez-Aulet JP, Giri N, Dai J, Steinberg M, Waterfall JP, Roberson D, Ballew BJ, Zhou W, Anzick SL, Jiang Y, Wang Y, Zhu YJ, Meltzer PS, Boland J, Alter BP, Savage SA (2019) 1q21.1 deletion and a rare functional polymorphism in siblings with thrombocytopenia-absent radius-like phenotypes. Cold Spring Harb Mol Case Stud 5(6) The first mutation is inheritance of a 1q21.1 deletion and the second is in the remaining in the

RBM8A RNA-binding protein 8A is a protein that in humans is encoded by the ''RBM8A'' gene. This gene encodes a protein with a conserved RNA-binding motif. The protein is found predominantly in the nucleus, although it is also present in the cytoplasm. ...

gene. Approximately 95% of TAR patients have one non-functional copy of the RBM8A gene.

Treatment

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 ''In Utero'' is the third and final studio album by American rock band Nirvana. It was released on September 21, 1993, by DGC Records. After breaking into the mainstream with their second album, ''Nevermind'' (1991), Nirvana hired Steve Albin ...

. 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.

Epidemiology

The incidence is 0.42 per 100,000 live births.

History

In 1929 Greenwald and Sherman{{ described the first patient with TAR Syndrome. 40 years later Hall collected 40 cases and introduced the name "Thrombocytopenia with absent radius". In 1988 Hedberg published an article with 100 cases.{{cite journal , vauthors = Hedberg VA, Lipton JM , title = Thrombocytopenia with absent radii. A review of 100 cases , journal = The American Journal of Pediatric Hematology/Oncology , volume = 10 , issue = 1 , pages = 51–64 , year = 1988 , pmid = 3056062 , department = review , doi = 10.1097/00043426-198821000-00010

References

{{reflist

External links

Thrombocytopenia Absent Radii research study of Inherited Bone Marrow Failure Syndromes (IBMFS)

GeneReview/NCBI/NIH/UW entry on Thrombocytopenia Absent Radius Syndrome
{{Medical resources , DiseasesDB = 29769 , ICD10 = {{ICD10, Q, 87, 2, q, 80 , ICD9 = {{ICD9, 287.33 , ICDO = , OMIM = 274000 , MedlinePlus = , eMedicineSubj = , eMedicineTopic = , MeshID = {{Multiple abnormalities {{Chromosomal abnormalities {{DEFAULTSORT:Tar Syndrome Autosomal monosomies and deletions Syndromes with dysmelia Syndromes affecting blood Rare syndromes