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Congenital myotonic dystrophy — RACP Paediatrics MCQ

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HardNeurologyCongenital myotonic dystrophyRACP Paediatrics

A term neonate has hypotonia, a weak suck, and a tented upper lip (inverted V-shape). The mother is noted to have facial weakness, distal muscle wasting, grip myotonia, and cataracts. The baby requires prolonged ventilatory support. What is the most likely diagnosis?

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Correct answer: C — Congenital myotonic dystrophy

Congenital myotonic dystrophy type 1 is suspected when a hypotonic neonate is born to a mother with myotonic dystrophy (DM1). The tented upper lip (myopathic facies) is characteristic. Congenital DM1 is caused by massive CTG repeat expansion in the DMPK gene and is inherited maternally (genetic anticipation). Respiratory support may be required for weeks to months.

Reference: RCH Melbourne – 2023 – Floppy Infant CPG; RACP Paediatric Curriculum – Neurology/Genetics