Diamond–Blackfan Anemia (DBA) Practice Flashcards

Overview and Definition of Diamond–Blackfan Anemia (DBA)

• Definition: Diamond–Blackfan anemia (DBA) is defined as a rare congenital pure red cell aplasia (PRCA).

• Key Characteristics:

  • Failure of erythropoiesis within the bone marrow.

  • Severe macrocytic anemia that typically presents in infancy.

  • Measurement of White Blood Cell (WBC) and platelet counts typically yields normal results.

  • Association with various congenital anomalies.

• High-Yield Fact: DBA stands as the most common inherited cause of pure red cell aplasia identified in pediatric populations.

Etiology and Genetic Basis

• Inheritance Pattern: The condition usually follows an autosomal dominant inheritance pattern.

• Genetic Mutations: The primary cause involves mutations in genes that encode for ribosomal proteins.

• Common Genetic Indicators: The most frequently identified mutation occurs in the $RPS19$ gene.

• Classification: Within medical pathology, DBA is classified as a "ribosomopathy."

Pathogenesis of DBA

• Ribosomal Protein Defects: Defects in ribosomal proteins trigger a cascade of cellular failures:

  1. Impaired Ribosome Synthesis: The cell is unable to produce ribosomes at a normal rate or quality.

  2. Increased Apoptosis: There is a marked increase in the programmed cell death of erythroid progenitor cells.

  3. Erythropoietic Failure: Consequently, the production of red blood cells (RBCs) fails.

• Physiological Result: This results in a marked reduction of erythroid precursors within the bone marrow and the subsequent development of severe anemia.

Clinical Presentation and Symptoms

• Age of Presentation:

  • Symptoms usually manifest before the infant reaches $1$ year of age.

  • The vast majority of cases are diagnosed within the first $6$ months of life.

• Symptoms of Anemia:

  • Pallor (paleness).

  • Irritability.

  • Feeding difficulties.

  • Failure to thrive.

  • Tachycardia (increased heart rate).

  • Lethargy.

Associated Congenital Anomalies

Approximately $50\%$ of patients with DBA present with congenital anomalies across various systems:

• Craniofacial Anomalies:

  • Cleft palate.

  • Hypertelorism (increased distance between the eyes).

  • Flat nasal bridge.

  • Micrognathia (undersized jaw).

• Upper Limb Abnormalities:

  • Triphalangeal thumb: A thumb with three phalanges instead of two.

  • Hypoplastic thumb (underdeveloped).

  • Absent thumb.

• Growth Issues:

  • Short stature.

• Cardiac Defects:

  • Atrial Septal Defect (ASD).

  • Ventricular Septal Defect (VSD).

• Genitourinary Anomalies:

  • Renal (kidney) anomalies.

  • Hypospadias.

• High-Yield Diagnostic Pearl: The combination of thumb abnormalities and severe anemia in an infant should immediately suggest a diagnosis of DBA.

Laboratory Investigations and Diagnostic Markers

• Complete Blood Count (CBC):

  • Low Hemoglobin ($Hb$).

  • Macrocytic anemia (elevated Mean Corpuscular Volume, MCV).

  • Normal White Blood Cell (WBC) count.

  • Normal Platelet count.

• Reticulocyte Count: Markedly reduced or near-absent.

• Peripheral Blood Film (PBF): Reveals macrocytosis and reticulocytopenia.

• Bone Marrow Examination:

  • Demonstrates a marked reduction or complete absence of erythroid precursors.

  • Granulopoiesis (white cell production) is normal.

  • Megakaryocytes (platelet precursors) are normal.

• Biochemical Markers:

  • Increased Fetal Hemoglobin ($HbF$).

  • Increased erythrocyte Adenosine Deaminase ($eADA$).

• Genetic Testing: Targeted testing for mutations in ribosomal protein genes.

Classical Diagnostic Criteria

Diagnosis is generally established when the following classical findings are present:

1. Age at onset less than $1$ year.

2. Macrocytic anemia.

3. Reticulocytopenia (low reticulocyte count).

4. Normal WBC and platelet counts.

5. Bone marrow biopsy/aspiration showing erythroid hypoplasia.

Differential Diagnosis

• Transient Erythroblastopenia of Childhood (TEC): Unlike DBA, this is an acquired condition that typically affects older children (ages $1-4$).

• Aplastic Anemia: Characterized by pancytopenia (reduction in all blood cell lines) rather than pure red cell aplasia.

• Fanconi Anemia: Characterized by pancytopenia and chromosomal breakage; often presents with similar physical anomalies but different hematologic progression.

• Iron Deficiency Anemia: Characterized by microcytic anemia, whereas DBA is macrocytic.

• Pure Red Cell Aplasia (PRCA) Secondary to Parvovirus B19: An acquired infection that causes a temporary halt in RBC production.

Comparison: DBA vs. TEC (Favorite Viva Topic)

Management and Treatment Strategies

First-Line Treatment

• Corticosteroids (Prednisolone): Used to improve erythropoiesis. Many patients show a positive response and improved hemoglobin levels.

Supportive Care

• Blood Transfusions: Required for patients with severe anemia to maintain adequate hemoglobin levels for growth and development.

• Iron Chelation Therapy: Necessary for patients receiving repeated transfusions to prevent iron overload. Agents include:

  • Deferasirox.

  • Deferoxamine.

Curative Treatment

• Hematopoietic Stem Cell Transplantation (HSCT): This is the only definitive cure for DBA. It is the preferred option for patients who become transfusion-dependent.

Complications and Risks

• Disease-Related Complications:

  • Growth retardation.

  • Developmental delay.

• Transfusion-Related Complications:

  • Iron overload (hemosiderosis).

  • Cardiac failure secondary to iron deposition.

  • Liver dysfunction.

• Treatment-Related Complications (Steroid Toxicity):

  • Osteoporosis.

  • Cataracts.

• Malignancy Risk: Patients have an increased risk of developing:

  • Acute Myeloid Leukemia (AML).

  • Myelodysplastic Syndrome (MDS).

  • Osteogenic sarcoma.

Prognosis

• The prognosis is variable among patients.

• Some patients achieve long-term remission or remain steroid-responsive.

• Others remain transfusion-dependent and require ongoing chelation.

• HSCT provides the best chance for a definitive cure.

Exam Pearls and Mnemonics

• What is DBA?: Congenital pure red cell aplasia resulting from ribosomal protein gene mutations.

• Common Mutation: $RPS19$.

• Bone Marrow: Specific absence of erythroid precursors.

• Blood Picture: Macrocytic anemia paired with reticulocytopenia.

• Classic Anomaly: Thumb abnormalities.

• Definitive Treatment: Hematopoietic Stem Cell Transplantation (HSCT).

Mnemonic: "DIAMOND"

• D – Defective ribosomes

• I – Infantile onset

• A – Absent erythroid precursors

• M – Macrocytic anemia

• O – Often thumb anomalies

• N – Normal WBC and platelets

• D – Dominant inheritance (often Autosomal Dominant)

High-Yield Summary Table for MBBS Finals