Thrombocytopenia-Absent Radius Syndrome (TAR)

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MedlinePlus Genetics: ⁴² Thrombocytopenia-absent radius (TAR) syndrome is characterized by the absence of a bone called the radius in each forearm and a shortage (deficiency) of blood cells involved in clotting (platelets). This platelet deficiency (thrombocytopenia) usually appears during infancy and becomes less severe over time; in some cases the platelet levels become normal.Thrombocytopenia prevents normal blood clotting, resulting in easy bruising and frequent nosebleeds. Potentially life-threatening episodes of severe bleeding (hemorrhages) may occur in the brain and other organs, especially during the first year of life. Hemorrhages can damage the brain and lead to intellectual disability. Affected children who survive this period and do not have damaging hemorrhages in the brain usually have a normal life expectancy and normal intellectual development.The severity of skeletal problems in TAR syndrome varies among affected individuals. The radius, which is the bone on the thumb side of the forearm, is almost always missing in both arms. The other bone in the forearm, which is called the ulna, is sometimes underdeveloped or absent in one or both arms. TAR syndrome is unusual among similar malformations in that affected individuals have thumbs, while people with other conditions involving an absent radius typically do not. However, there may be other abnormalities of the hands, such as webbed or fused fingers (syndactyly) or curved pinky fingers (fifth finger clinodactyly). Some people with TAR syndrome also have skeletal abnormalities affecting the upper arms, legs, or hip sockets.Other features that can occur in TAR syndrome include malformations of the heart or kidneys. Some people with this disorder have unusual facial features including a small lower jaw (micrognathia), a prominent forehead, and low-set ears. About half of affected individuals have allergic reactions to cow's milk that may worsen the thrombocytopenia associated with this disorder.

MalaCards based summary: Thrombocytopenia-Absent Radius Syndrome, also known as tar syndrome, is related to thrombocytopenia and chromosome 1q21.1 deletion syndrome, 1.35-mb. An important gene associated with Thrombocytopenia-Absent Radius Syndrome is RBM8A (RNA Binding Motif Protein 8A), and among its related pathways/superpathways are Embryonic and Induced Pluripotent Stem Cells and Lineage-specific Markers and Visual Cycle in Retinal Rods. Affiliated tissues include bone, bone marrow and kidney, and related phenotypes are thrombocytopenia and abnormality of coagulation

OMIM®: ⁵⁷ The thrombocytopenia-absent radius syndrome (TAR) is characterized by reduction in the number of platelets and absence of the radius; preservation of the thumb distinguishes TAR from other syndromes that combine blood abnormalities with absence of the radius, such as Fanconi anemia (see 227650). Individuals with TAR have low numbers of megakaryocytes, platelet precursor cells that reside in bone marrow, and frequently present with bleeding episodes in the first year of life that diminish in frequency and severity with age. The severity of skeletal anomalies varies from absence of radii to virtual absence of upper limbs, with or without lower limb defects such as malformations of the hip and knee (summary by Albers et al., 2012). (274000) (Updated 24-Oct-2022)

GARD: ¹⁹ 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. 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.

Disease Ontology: ¹¹ A chromosomal deletion syndrome that is characterized by absence of the radius bone and platelet deficiency and bilateral absence of the radii with the presence of both thumbs and generally transient thrombocytopenia (less than 50 platelets/nL) and that has material basis in compound heterozygosity for a rare null mutation involving the RBM8A gene on chromosome 1q12 on 1 allele and 1 of 2 low-frequency noncoding single-nucleotide polymorphisms in RBM8A on the other.

UniProtKB/Swiss-Prot: ⁷³ An autosomal recessive disorder characterized by bilateral absence of the radii with the presence of both thumbs, thrombocytopenia, low numbers of megakaryocytes, and bleeding episodes in the first year of life. Thrombocytopenic episodes decrease with age. Skeletal anomalies range from absence of radii to virtual absence of upper limbs, with or without lower limb defects such as malformations of the hip and knee.

Orphanet: ⁵⁸ Thrombocytopenia-absent radius (TAR) syndrome is a very rare congenital malformation syndrome characterized by bilateral radial aplasia and thrombocytopenia.

Wikipedia: ⁷⁵ TAR syndrome (thrombocytopenia with absent radius) is a rare genetic disorder that is characterized by... more...

Clinical features from OMIM®:

Search Clinical Trials, NIH Clinical Center for Thrombocytopenia-Absent Radius Syndrome