TAR syndrome
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TAR syndrome (thrombocytopenia with absent radius) is a rare genetic disorder that is characterized by the absence of the radius bone in the forearm and a dramatically reduced platelet count.<ref name="Toriello_2016">Template:Cite book</ref> It is associated with cardiac defects, dysmorphic features, and petechiae. It involves a 1q21 deletion with RMB8A variant on other allele.<ref name="Petit 2009">Template:Cite journal</ref>
Signs and symptoms
- Presents with symptoms of thrombocytopenia, or a lowered platelet count, leading to bruising and potentially life-threatening hemorrhage.<ref>Template:Cite journal</ref>
- Absence of the radius bone in the forearm with preservation of the thumbTemplate:Citation needed.
Other common links between people with TAR syndrome include anemia, heart problems, kidney problems, knee joint problems, and frequently milk allergy. Different cases with leukemia in patients with TAR are described in.Template:Clarify<ref>Template:Cite journal</ref>
Genetics
This condition requires mutations in both chromosomesTemplate:Clarify.<ref name=Brodie2019>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)</ref> The first mutation is inheritance of a 1q21.1 deletion and the second is in the remaining in the RBM8A gene.
Approximately 95% of TAR patients have one non-functional copy of the RBM8A gene.<ref name="pmid23602329">Template:Cite journal</ref><ref name="pmid27981927">Template:Cite journal</ref>
Treatment
Treatments range from platelet transfusions<ref name="Toriello_2016" /> 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'.Template:Citation needed There is some controversy surrounding the role of surgeryTemplate:Citation needed. The infant mortality rate has been curbed by new technology, including platelet transfusions, which can even be performed in uteroTemplate:Citation needed. The critical period is the first and sometimes second year of lifeTemplate:Citation needed. For most people with TAR, platelet counts improve as they grow out of childhood.Template:Citation needed
Epidemiology
The incidence is 0.42 per 100,000 live birthsTemplate:Citation needed.
History
In 1929 Greenwald and Sherman described the first patient with TAR Syndrome.<ref>Template:Cite journal</ref> 40 years later Hall collected 40 cases and introduced the name "Thrombocytopenia with absent radius".<ref>Template:Cite journal</ref> In 1988 Hedberg published an article with 100 cases.<ref>Template:Cite journal</ref>
References
Further reading
External links
- Thrombocytopenia Absent Radii research study of Inherited Bone Marrow Failure Syndromes (IBMFS)
- GeneReview/NCBI/NIH/UW entry on Thrombocytopenia Absent Radius Syndrome
Template:Medical resources Template:Multiple abnormalities Template:Chromosomal abnormalities