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Spinal muscular atrophy SMN1 deletion — MRCPCH TAS MCQ

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HardGeneticsSpinal muscular atrophy SMN1 deletionMRCPCH TAS

A 3-month-old has poor head control, tongue fasciculations and symmetrical weakness. Deep tendon reflexes are absent and creatine kinase is not markedly raised. What is the most appropriate investigation?

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Correct answer: C — SMN1 deletion testing

Tongue fasciculations, hypotonia and areflexia suggest spinal muscular atrophy, best confirmed by SMN1 deletion testing. Dystrophin testing would fit Duchenne muscular dystrophy, which usually presents later with very high creatine kinase. The pearl is that SMA is a motor neuron disorder rather than a primary myopathy.

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