TAR SYNDROME
 
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TAR SYNDROME

 

DEFINITION:

Thrombocytopenia-Absent Radii (TAR) Syndrome is characterized by the neonatal onset of thrombocytopenia and bilateral absence or hypoplasia of the radii with normal thumbs.

EPIDEMIOLOGY:

  • incidence: rare
  • age of onset:
    • thrombocytopenia within first 4 months of life
  • risk factors:
    • familial - autosomal recessive
      • chrom.#: ?
      • gene: ?
    • F > M (7:5)

PATHOGENESIS:

  • one of at least 3 autosomal recessive syndromes associated with hematopoietic and skeletal anomalies:
    • AASE Syndrome
    • Fanconi Anemia
  • one of at least 4 disorders associated with radial agenesis:
    • Baller-Gerold Syndrome
    • Fanconi Anemia
    • Holt-Oram Syndrome
    • VATER Association
  • gene defect in early gestation (between 4-8 weeks) -> disrupts formation of the radii, the heart, and hematopoiesis

CLINICAL FEATURES:

1. Thrombocytopenia

  • onset in newborn period but tends to improve with age
  • episodes precipitated by stress, infections, surgery, and cow's milk allergy
    • bloody stool
    • hematemesis
    • hemorrhage
    • intracranial bleeds
    • nosebleeds
    • purpura

2. Musculoskeletal Manifestations

  • short stature
  • radii - bilateral hypoplasia or aplasia with normal thumbs
  • ulnae - hypoplasia or aplasia
  • humerus - aplasia (50%) -> phocomelia
  • defects of hands, legs, and/or feet
  • others - congenital dislocation of the hips, subluxation and stiffness of knees, dislocated patellae

3. Others

  • cardiac anomalies (30%) - Tetralogy of Fallot, Atrial Septal Defect
  • hepatomegaly/hepatosplenomegaly (during leukemoid reactions)
  • normal psychomotor development

INVESTIGATIONS:

1. Serum

  • platelets - <100 with reduced aggregation and survival
  • "leukemoid" granulocytosis (60-70%) in first year of life with WBC > 35
  • anemia

2. Bone Marrow

  • megakaryocytes
    • absent (66%), decreased (12%), inactive (12%)
    • small, basophilic, vacuolated, nongranulated
  • eosinophilia (53%)

3. Imaging Studies

1. Skeletal X-rays

  • upper limbs

2. Prenatal Ultrasound

  • affected ulnae from 16 weeks in utero

4. Chromosomal Breakage Analysis

  • normal

MANAGEMENT:

1. Supportive

  • transfusions of platelets, whole blood products
  • avoid infections, stress, surgery, cow's milk
  • corrective orthopedic braces for forearms
  • thrombocytopenia improves with age
  • normal lifespan if child survives the first 2 years

 

Pediatric Database - TAR SYNDROME

 

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