DiGeorge syndrome vs Velocardiofacial syndrome and CATCH-22 framing
How to tell DiGeorge syndrome and Velocardiofacial syndrome and CATCH-22 framing apart when a board question makes them look alike.
DiGeorge spotlights thymus/parathyroid/T-cell hypocalcemia; velocardiofacial spotlights palate/facies/psychiatric features; both are 22q11.2 deletion spectrum.
Side by side
DiGeorge syndrome classically emphasizes thymic aplasia, T-cell deficiency, hypocalcemia from parathyroid aplasia, conotruncal defects, and 22q11.2 deletion.
Velocardiofacial syndrome emphasizes palatal abnormalities, characteristic facies, learning/psychiatric risk, and the same 22q11.2 deletion spectrum; CATCH-22 is a memory cluster for the shared deletion.
Failed development of third and fourth pharyngeal pouches disrupts thymus and parathyroids.
Variable 22q11.2 deletion expression affects pharyngeal arch/pouch derivatives, palate, heart, face, calcium, and neuropsychiatric phenotype.
Low T cells, absent thymic shadow, hypocalcemic tetany, and conotruncal heart defect support DiGeorge presentation.
Cleft palate, velopharyngeal insufficiency, nasal speech, and psychiatric risk support velocardiofacial-predominant presentation.
The trap
These are not completely separate genes; the exam often changes which 22q11.2 feature cluster it highlights.
The repair move
For 22q11.2, identify whether the stem is testing immune-calcium-heart findings or palate/facial/neuropsychiatric findings.
Try a free question
CoreA 2-week-old newborn presents with hypocalcemic tetany (calcium 6.2 mg/dL) with seizures, truncus arteriosus on echocardiogram, an absent thymic shadow on chest X-ray, and recurrent severe Candida and viral infections. FISH analysis confirms a 22q11.2 deletion. Which condition is most likely?
Show answer and explanation
Answer: A. DiGeorge syndrome. DiGeorge syndrome: failed development of the 3rd and 4th pharyngeal pouches produces thymic aplasia (T-cell deficiency with viral/fungal infections), parathyroid aplasia (hypocalcemia, tetany), and conotruncal heart defects (truncus arteriosus, tetralogy of Fallot, interrupted aortic arch). 22q11.2 deletion is the cause.
Why the other choices are tempting
- B. SCID has profound combined T and B cell deficiency from various genetic causes but does not classically include conotruncal heart defects or hypocalcemia.
- C. Chronic granulomatous disease has NADPH oxidase deficiency with catalase-positive organism infections (Staphylococcus aureus, Aspergillus), not the DiGeorge triad.
- D. Wiskott-Aldrich syndrome has X-linked thrombocytopenia, eczema, and immunodeficiency, not conotruncal heart defects with hypocalcemia.
- E. Hyper-IgM syndrome has CD40L deficiency with high IgM, low other immunoglobulin classes, and recurrent pyogenic infections, not the DiGeorge phenotype.
Flashcards
Tap a card to flip it.
What clue supports DiGeorge syndrome?
Choose DiGeorge syndrome when the stem gives this pattern: DiGeorge syndrome classically emphasizes thymic aplasia, T-cell deficiency, hypocalcemia from parathyroid aplasia, conotruncal defects, and 22q11.2 deletion.
What clue supports Velocardiofacial syndrome and CATCH-22 framing?
Choose Velocardiofacial syndrome and CATCH-22 framing when the stem gives this contrasting pattern: Velocardiofacial syndrome emphasizes palatal abnormalities, characteristic facies, learning/psychiatric risk, and the same 22q11.2 deletion spectrum; CATCH-22 is a memory cluster for the shared deletion.
Quick answers
What is the fastest way to tell DiGeorge syndrome from Velocardiofacial syndrome and CATCH-22 framing?
DiGeorge spotlights thymus/parathyroid/T-cell hypocalcemia; velocardiofacial spotlights palate/facies/psychiatric features; both are 22q11.2 deletion spectrum.
What is the key clue for DiGeorge syndrome?
DiGeorge syndrome classically emphasizes thymic aplasia, T-cell deficiency, hypocalcemia from parathyroid aplasia, conotruncal defects, and 22q11.2 deletion.
What is the key clue for Velocardiofacial syndrome and CATCH-22 framing?
Velocardiofacial syndrome emphasizes palatal abnormalities, characteristic facies, learning/psychiatric risk, and the same 22q11.2 deletion spectrum; CATCH-22 is a memory cluster for the shared deletion.
What is the common trap with DiGeorge syndrome vs Velocardiofacial syndrome and CATCH-22 framing?
These are not completely separate genes; the exam often changes which 22q11.2 feature cluster it highlights.