✅ Model Answer:
• Bilateral absence of the radius (radial aplasia).
• Shortened, bowed ulna (may be present).
• Hand deviated radially (clubhand deformity).
• Normal humerus (proximal bone intact).
• Bilateral involvement – characteristic of TAR syndrome.
• Diagnosis: Thrombocytopenia with Absent Radius (TAR syndrome).

✅ Model Answer:
• TAR syndrome (Thrombocytopenia with Absent Radius) is a rare congenital disorder.
• Key features:
1. Bilateral radial aplasia – absence of the radius bone in both forearms.
2. Thrombocytopenia – platelet count usually <50,000/μL, present at birth.
3. Bowed ulna – the ulna is often short and curved.
4. Radial deviation of the hand – clubhand deformity.
5. Bone marrow – decreased or absent megakaryocytes.
6. Other anomalies: Cardiac defects (VSD, ASD), gastrointestinal issues, cow's milk allergy (common).
7. Thrombocytopenia improves with age – typically by 1-2 years.

✅ Model Answer:

Feature	TAR Syndrome	Fanconi Anemia
Radial aplasia	Bilateral	May be unilateral
Thrombocytopenia	Present (improves with age)	Progressive pancytopenia
Marrow	Decreased megakaryocytes	Hypoplastic, progressive
Chromosome fragility	No	Yes (DEB positive)
Associated anomalies	Cardiac, GI, cow's milk allergy	Renal, cardiac, microcephaly, thumb anomalies

✅ Model Answer:
• Thrombocytopenia in TAR syndrome is due to decreased production of platelets in the bone marrow.
• Bone marrow biopsy shows decreased or absent megakaryocytes.
• The defect is thought to be intrinsic to the megakaryocyte lineage (impaired maturation/differentiation).
• Platelet survival is normal – the defect is in production, not destruction.
• Thrombocytopenia is present at birth and is most severe in the first year of life.
• Improves with age: Platelet counts typically rise to normal or near-normal levels by 1-2 years of age.
• Unlike Fanconi anemia, there is no progression to aplastic anemia or leukemia.

✅ Model Answer:
• Skeletal: Bilateral absence of the radius, short bowed ulnae, radial deviation of the hands, normal thumbs (distinguishes from Fanconi anemia).
• Hematological: Thrombocytopenia – petechiae, bruising, bleeding (GI bleeding, intracranial hemorrhage).
• Associated anomalies: Congenital heart defects (VSD, ASD, TOF), gastrointestinal (malrotation, imperforate anus), genitourinary abnormalities.
• Feeding: Cow's milk allergy (common) – presents with vomiting, diarrhea, failure to thrive.
• Growth: Growth restriction (intrauterine and postnatal).
• Intelligence: Usually normal (unlike some other syndromes with radial anomalies).

✅ Model Answer:
• Diagnosis is based on the combination of:
1. Clinical features: Bilateral radial aplasia + thrombocytopenia.
2. X-ray findings: Bilateral absent radius, short bowed ulna.
3. Hematological findings: Thrombocytopenia (platelets <50,000/μL).
4. Bone marrow biopsy: Decreased or absent megakaryocytes (confirmatory).
• Genetic testing: TAR syndrome is associated with 1q21.1 microdeletion or RBM8A mutations (in some cases).
• Differential diagnosis:
- Fanconi anemia (chromosome fragility, progressive pancytopenia).
- Radial aplasia with thrombocytopenia (other syndromes).
- Isolated radial aplasia (no thrombocytopenia).

✅ Model Answer:
• Platelet transfusions:
- Indicated for bleeding (petechiae, bruising, GI bleeding, intracranial hemorrhage).
- Prophylactic transfusions are NOT recommended unless the patient is actively bleeding or undergoing invasive procedures.
• Avoid:
- Antiplatelet medications (aspirin, NSAIDs).
- Intramuscular injections (risk of hematoma).
• Monitor:
- Serial platelet counts – most improve by 1-2 years of age.
- Watch for signs of bleeding (petechiae, bruising, melena, hematuria).
• Special precautions:
- Use a soft toothbrush, avoid trauma.
- Circumcision should be delayed until platelet count improves.

✅ Model Answer:
• Non-surgical management:
- Physical therapy – range of motion exercises, splinting.
- Functional adaptation – hand therapy to optimize use.
• Surgical management (for functional improvement):
- Centralization – surgical repositioning of the hand over the distal ulna to improve alignment.
- Usually performed at 6-12 months of age (once platelet count has improved).
- Goals: Improve hand function, cosmesis, and prevent progressive deformity.
• Prosthetics: May be considered for cosmetic purposes (not usually functional).
• Multidisciplinary approach: Orthopedic surgeon + physical therapist + occupational therapist.

✅ Model Answer:
• This is a bleeding emergency due to severe thrombocytopenia.
• Management:
1. Platelet transfusion – immediate transfusion to raise platelet count and stop bleeding.
2. IV fluids – for volume resuscitation if hypotensive.
3. Blood transfusion – if significant blood loss (hemoglobin drop).
4. GI evaluation – determine the source of bleeding (upper vs lower GI).
5. Transfusion threshold: Platelet count <20,000 or <50,000 with active bleeding.
6. Prevent recurrence: Monitor platelet count, treat underlying thrombocytopenia.

✅ Model Answer:
• Cow's milk allergy is common in TAR syndrome (up to 50% of patients).
• Management:
1. Dietary modification: Strict avoidance of cow's milk and dairy products.
2. Use hydrolyzed formula (e.g., extensively hydrolyzed casein formula) or amino acid-based formula.
3. Monitor for symptoms: Vomiting, diarrhea, failure to thrive, GI bleeding.
4. Reassess tolerance: Cow's milk allergy may improve with age.
5. Nutritional support: Ensure adequate calcium and vitamin D intake (supplementation if needed).

✅ Model Answer:
• Thrombocytopenia improves with age – most children have normal platelet counts by 1-2 years of age.
• Bone anomalies: Function of the upper limbs may be improved with surgical centralization.
• Cognitive development: Usually normal – children with TAR syndrome have normal intelligence.
• Mortality: Highest in the first year of life (intracranial hemorrhage, GI bleeding, cardiac anomalies).
• Long-term: With supportive care, most children lead productive lives. Regular follow-up with hematology, orthopedics, and cardiology is essential.
• Recurrence risk: Autosomal recessive inheritance (for 1q21.1 deletion-associated cases).