DiGeorge syndrome

• Definition: syndrome characterized by defective development of the third and fourth pharyngeal pouches leading to hypoplastic thymus and parathyroids
• Etiology: autosomal dominant; microdeletion at chromosome 22 (22q11.2)
• Clinical features
  • Cardiac anomalies
    • Conotruncal abnormalities (e.g., tetralogy of Fallot or persistent truncus arteriosus)
    • Ventricular septal defect (VSD)
    • Atrial septal defect (ASD)
  • Anomalous face
    • Prominent nasal bridge
    • Hypoplastic wing of the nose
    • Dysplastic ears
    • Micrognathia (small lower jaw) and/or retrognathia
  • Thymus aplasia/hypoplasia: recurrent infections (viral/fungal/PCP pneumonia) due to T-cell deficiency c
  • Cleft palate
  • Hypoparathyroidism: hypocalcemia with tetany
• Diagnosis
  • Detection of 22q11.2 deletion via fluorescence in situ hybridization (FISH)
  • ↓ PTH and Ca²⁺
  • ↓ Absolute T-lymphocyte count
  • Delayed hypersensitivity skin testing
  • CXR: absence of thymic shadow

Mnemonic

CATCH-22 is the acronym for typical features of DiGeorge syndrome: Cardiac anomalies; Anomalous face; Thymic aplasia/hypoplasia; Cleft palate; Hypocalcemia; Chromosome 22.