TAR syndrome
Encyclopedia
TAR Syndrome 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
, 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
. The critical period is the first year of life. For most people with TAR, platelet counts improve as they grow out of childhood.
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, so there are likely other genetic components of the syndrome besides this one, hence when a child has the condition any future siblings are likely to have a 25% chance of also having it.
Genetic disorder
A genetic disorder is an illness caused by abnormalities in genes or chromosomes, especially a condition that is present from before birth. Most genetic disorders are quite rare and affect one person in every several thousands or millions....
that is characterized by the absence of the radius bone
Radius (bone)
The radius 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, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...
in the forearm, and a dramatically reduced platelet
Platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days...
count. This syndrome may occur as a part of the 1q21.1 deletion syndrome
1q21.1 deletion syndrome
1q21.1 deletion syndrome or 1q21.1 microdeletion is a rare aberration of chromosome 1. , the international rare chromosome disorder group, has 48 genetically confirmed registered cases of this deletion worldwide ....
Presentation
Symptoms of thrombocytopeniaThrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...
, or a lowered platelet count, leads to bruising and potentially life-threatening hemorrhage.
Other common links between people with TAR seem to include heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
problems, kidney
Kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...
problems, knee joint problems, frequently lactose intolerance
Lactose intolerance
Lactose intolerance, also called lactase deficiency or hypolactasia, is the inability to digest and metabolize lactose, a sugar found in milk...
and often thumb hypoplasia
Thumb hypoplasia
Thumb hypoplasia is a spectrum of congenital abnormalities of the thumb varying from small defects to complete absence of the thumb. It can be isolated, when only the thumb is affected, and in 59% of the cases it is associated with radial dysplasia...
Treatment
Treatments range from platelet transfusions to surgery 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 uteroIn utero
In utero is a Latin term literally meaning "in the womb". In biology, the phrase describes the state of an embryo or fetus. In legal contexts, the phrase is used to refer to unborn children. Under common law, unborn children are still considered to exist for property transfer purposes.-See also:*...
. The critical period is the first year of life. For most people with TAR, platelet counts improve as they grow out of childhood.
Genetics
Genetic research is underway. A 2007 research article identified a region of chromosomeChromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
1, 1q21.1, containing 11 genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
(including HFE2
Hemojuvelin
Hemojuvelin is a membrane-bound and soluble protein in mammals that is responsible for the iron overload condition known as juvenile hemochromatosis in humans, a severe form of hemochromatosis. In humans, the hemojuvelin protein is encoded by the HFE2 gene...
, LIX1L
LIX1L
Lix1 homolog -like also known as LIX1L is a protein which in humans is encoded by the LIX1L gene.-Related gene problems:*TAR syndrome*1q21.1 deletion syndrome*1q21.1 duplication syndrome...
, PIAS3
PIAS3
E3 SUMO-protein ligase PIAS3 is an enzyme that in humans is encoded by the PIAS3 gene.-Interactions:PIAS3 has been shown to interact with GFI1, RELA, Mothers against decapentaplegic homolog 3, Microphthalmia-associated transcription factor, HMGA2 and Mothers against decapentaplegic homolog...
, ANKRD35
ANKRD35
Ankyrin repeat domain 35 also known as ANKRD35 is a protein which in humans is encoded by the ANKRD35 gene.-Related gene problems:*TAR syndrome*1q21.1 deletion syndrome*1q21.1 duplication syndrome...
, ITGA10
ITGA10
Integrin alpha-10 also known as ITGA10 is a protein that in humans is encoded by the ITGA10 gene.-Function:Integrins are integral membrane proteins composed of an alpha chain and a beta chain, and are known to participate in cell adhesion as well as cell-surface mediated signalling...
, RBM8A
RBM8A
RNA-binding protein 8A is a protein that in humans is encoded by the RBM8A gene.-Interactions:RBM8A has been shown to interact with IPO13, MAGOH and UPF3A.-Related gene problems:*TAR syndrome*1q21.1 deletion syndrome*1q21.1 duplication syndrome...
, PEX11B
PEX11B
Peroxisomal membrane protein 11B is a protein that in humans is encoded by the PEX11B gene. It is involved in the regulation of peroxisome abundance.-Related gene problems:*TAR syndrome*1q21.1 deletion syndrome*1q21.1 duplication syndrome...
, POLR3GL
POLR3GL
Polymerase III polypeptide G -like also known as POLR3GL is a protein which in humans is encoded by the POLR3GL gene.-Related gene problems:*TAR syndrome*1q21.1 deletion syndrome*1q21.1 duplication syndrome...
, TXNIP
TXNIP
Thioredoxin-interacting protein is a protein that in humans is encoded by the TXNIP gene.-Interactions:TXNIP has been shown to interact with Thioredoxin and ZBTB32.-Related gene problems:*TAR syndrome*1q21.1 deletion syndrome...
, and GNRR2), that is heterozygously deleted in thirty of thirty patients with TAR. This deletion was also found in 32% of unaffected family members, so there are likely other genetic components of the syndrome besides this one, hence when a child has the condition any future siblings are likely to have a 25% chance of also having it.