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22q11.2 deletion testing — MRCPCH TAS MCQ

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HardGenetics22q11.2 deletion testingMRCPCH TAS

A newborn has truncus arteriosus, hypocalcaemic seizures and a small thymic shadow on chest radiograph. Lymphocyte subsets show low T-cell numbers. What is the most appropriate investigation?

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Correct answer: E — Chromosomal microarray for 22q11.2 deletion

Conotruncal heart disease, hypocalcaemia and thymic hypoplasia point to 22q11.2 deletion syndrome, now commonly detected by chromosomal microarray. Sweat chloride testing would investigate cystic fibrosis and would not explain T-cell lymphopenia. The key teaching point is that neural crest and pharyngeal pouch development are central to this phenotype.

Reference: RCPCH Theory examination syllabi; Nelson Textbook of Pediatrics; Lissauer's Illustrated Textbook of Paediatrics