TAR syndrome

TAR Syndrome (Thrombocytopenia with Absent Radius)
Classification and external resources
Specialty	medical genetics
ICD-10	Q87.2
ICD-9-CM	287.33
OMIM	274000
DiseasesDB	29769
[]

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. This syndrome may occur as a part of the 1q21.1 deletion syndrome

Symptoms of thrombocytopenia, or a lowered platelet count, leads to bruising and potentially life-threatening hemorrhage.

Other common links between people with TAR seem to include heart problems, kidney problems, knee joint problems, frequently lactose intolerance and often thumb hypoplasia

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. 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.

A 2007 research article identified a region of chromosome 1, 1q21.1, containing 11 genes (including HFE2, LIX1L, PIAS3, ANKRD35, ITGA10, RBM8A, PEX11B, POLR3GL, TXNIP, and GNRR2), that is heterozygously deleted in thirty of thirty patients with TAR. This deletion was also found in 32% of unaffected family members, indicating that the condition requires an additional modifier. In 2012, it was discovered that TAR syndrome is a recessive condition that is caused by the person with TAR syndrome having one allele with an abnormality in the RBM8A gene that reduces, but does not eliminate entirely, the production of the protein Y14 and the other allele with the RBM8A gene either absent (due to the microdeletion identified in 2009) or, less commonly, inoperative due to a different abnormality. The combination of these alleles reduces Y14 levels to a level that appears to result in the abnormalities characteristic of TAR syndrome.

...
Wikipedia