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Radial aplasia-thrombocytopenia syndrome(TAR)

MedGen UID:
61235
Concept ID:
C0175703
Congenital Abnormality
Synonyms: Absent radii and thrombocytopenia; TAR; TAR syndrome; Thrombocytopenia absent radii; Thrombocytopenia Absent Radius Syndrome
Modes of inheritance:
Autosomal recessive inheritance
MedGen UID:
141025
Concept ID:
C0441748
Intellectual Product
Sources: HPO, OMIM, Orphanet
A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in homozygotes. In the context of medical genetics, autosomal recessive disorders manifest in homozygotes (with two copies of the mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele).
Autosomal recessive inheritance (HPO, OMIM, Orphanet)
SNOMED CT: Thrombocytopenia with absent radius syndrome (85589009); TAR - Thrombocytopenia with absent radius syndrome (85589009); Radial aplasia-thrombocytopenia syndrome (85589009); Thrombocytopenia-absent radii syndrome (85589009); TAR syndrome (85589009)
 
Gene (location): RBM8A (1q21.1)
OMIM®: 274000

Disease characteristics

Excerpted from the GeneReview: Thrombocytopenia Absent Radius Syndrome
Thrombocytopenia absent radius (TAR) syndrome is characterized by bilateral absence of the radii with the presence of both thumbs and thrombocytopenia (<50 platelets/nL) that is generally transient. Thrombocytopenia may be congenital or may develop within the first few weeks to months of life; in general, thrombocytopenic episodes decrease with age. Cow’s milk allergy is common and can be associated with exacerbation of thrombocytopenia. Other anomalies of the skeleton (upper and lower limbs, ribs, and vertebrae), heart, and genitourinary system (renal anomalies and agenesis of uterus, cervix, and upper part of the vagina) can occur. [from GeneReviews]
Authors:
Helga V Toriello   view full author information

Additional descriptions

From OMIM
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).  http://www.omim.org/entry/274000
From GHR
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 cell fragments 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.  https://ghr.nlm.nih.gov/condition/thrombocytopenia-absent-radius-syndrome

Clinical features

Atrial septal defect
MedGen UID:
6753
Concept ID:
C0018817
Congenital Abnormality
Atrial septal defect (ASD) is a congenital abnormality of the interatrial septum that enables blood flow between the left and right atria via the interatrial septum.
Ventricular septal defect
MedGen UID:
42366
Concept ID:
C0018818
Congenital Abnormality
A hole between the two bottom chambers (ventricles) of the heart. The defect is centered around the most superior aspect of the ventricular septum.
Meckel diverticulum
MedGen UID:
9917
Concept ID:
C0025037
Congenital Abnormality
A congenital abnormality characterized by the outpouching or sac formation in the ILEUM. It is a remnant of the embryonic YOLK SAC in which the VITELLINE DUCT failed to close.
Micrognathia
MedGen UID:
44428
Concept ID:
C0025990
Congenital Abnormality
A congenital abnormality of the jaws (particularly the mandible) in which they are unusually small. This condition is not always pathological and may correct itself as the patient matures; however, it may also present as a birth defect in multiple syndromes.
Pancreatic cysts
MedGen UID:
45293
Concept ID:
C0030283
Disease or Syndrome
A cyst of the pancreas that possess a lining of mucous epithelium.
Seborrheic dermatitis
MedGen UID:
19912
Concept ID:
C0036508
Disease or Syndrome
A chronic inflammatory disease of the skin with unknown etiology. It is characterized by moderate ERYTHEMA, dry, moist, or greasy (SEBACEOUS GLAND) scaling and yellow crusted patches on various areas, especially the scalp, that exfoliate as dandruff. Seborrheic dermatitis is common in children and adolescents with HIV INFECTIONS.
Seizures
MedGen UID:
20693
Concept ID:
C0036572
Sign or Symptom
Clinical or subclinical disturbances of cortical function due to a sudden, abnormal, excessive, and disorganized discharge of brain cells. Clinical manifestations include abnormal motor, sensory and psychic phenomena. Recurrent seizures are usually referred to as EPILEPSY or "seizure disorder."
Spina bifida
MedGen UID:
38283
Concept ID:
C0080178
Congenital Abnormality
Spina bifida is a condition in which the neural tube, a layer of cells that ultimately develops into the brain and spinal cord, fails to close completely during the first few weeks of embryonic development. As a result, when the spine forms, the bones of the spinal column do not close completely around the developing nerves of the spinal cord. Part of the spinal cord may stick out through an opening in the spine, leading to permanent nerve damage. Because spina bifida is caused by abnormalities of the neural tube, it is classified as a neural tube defect.Children born with spina bifida often have a fluid-filled sac on their back that is covered by skin, called a meningocele. If the sac contains part of the spinal cord and its protective covering, it is known as a myelomeningocele. The signs and symptoms of these abnormalities range from mild to severe, depending on where the opening in the spinal column is located and how much of the spinal cord is affected. Related problems can include a loss of feeling below the level of the opening, weakness or paralysis of the feet or legs, and problems with bladder and bowel control. Some affected individuals have additional complications, including a buildup of excess fluid around the brain (hydrocephalus) and learning problems. With surgery and other forms of treatment, many people with spina bifida live into adulthood.In a milder form of the condition, called spina bifida occulta, the bones of the spinal column are abnormally formed, but the nerves of the spinal cord usually develop normally. Unlike in the more severe form of spina bifida, the nerves do not stick out through an opening in the spine. Spina bifida occulta most often causes no health problems, although rarely it can cause back pain or changes in bladder function.
Horseshoe kidney
MedGen UID:
65140
Concept ID:
C0221353
Congenital Abnormality
A congenital abnormality in which the two kidneys fuse together during fetal development to create a horseshoe-shaped structure.
Brachycephaly
MedGen UID:
113165
Concept ID:
C0221356
Congenital Abnormality
An abnormality of skull shape characterized by a decreased anterior-posterior diameter. That is, a cephalic index greater than 81%. Alternatively, an apparently shortened anteroposterior dimension (length) of the head compared to width.
Carpal synostosis
MedGen UID:
98468
Concept ID:
C0431863
Congenital Abnormality
Synostosis (bony fusion) involving one or more bones of the carpus (scaphoid, lunate, triquetrum, trapezium, trapezoid, capitate, hamate, pisiform).
Anteverted nares
MedGen UID:
326648
Concept ID:
C1840077
Finding
Anteriorly-facing nostrils viewed with the head in the Frankfurt horizontal and the eyes of the observer level with the eyes of the subject. This gives the appearance of an upturned nose (upturned nasal tip).
Motor delay
MedGen UID:
381392
Concept ID:
C1854301
Finding
A type of Developmental delay characterized by a delay in acquiring motor skills.
Shoulder muscle hypoplasia
MedGen UID:
369389
Concept ID:
C1969001
Finding
Underdevelopment of muscles of the shoulder.
Intellectual disability
MedGen UID:
811461
Concept ID:
C3714756
Mental or Behavioral Dysfunction
Subnormal intellectual functioning which originates during the developmental period. Intellectual disability, previously referred to as mental retardation, has been defined as an IQ score below 70.
Decreased antibody level in blood
MedGen UID:
892481
Concept ID:
C4048270
Finding
An abnormally decreased level of immunoglobulin in blood.

Term Hierarchy

CClinical test,  RResearch test,  OOMIM,  GGeneReviews,  VClinVar  
  • CROGVRadial aplasia-thrombocytopenia syndrome
Follow this link to review classifications for Radial aplasia-thrombocytopenia syndrome in Orphanet.

Recent clinical studies

Diagnosis

Hastings Cent Rep 1988 Aug-Sep;18(4):suppl 25-8. PMID: 3220743

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