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MCAD Deficiency — RACP Paediatrics MCQ

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ModerateGenetics & MetabolicMCAD DeficiencyRACP Paediatrics

An 18-month-old infant who was well until 12 hours ago becomes acutely encephalopathic after a period of fasting during a viral illness. Blood glucose is 1.2 mmol/L, plasma free fatty acids are elevated but ketones are inappropriately low. Acylcarnitine profile shows elevated octanoylcarnitine (C8). What is the most likely diagnosis?

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Correct answer: E — Fatty acid oxidation defect (MCAD deficiency)

Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency is the most common fatty acid oxidation defect, detected on newborn screening in Australia. It presents with hypoketotic hypoglycaemia during fasting or illness. Elevated C8 acylcarnitine on the acylcarnitine profile is diagnostic. Management is avoidance of prolonged fasting, emergency regimen during illness, and IV dextrose during acute decompensation.

Reference: RACP – 2024 – Paediatric Curriculum: Metabolic Medicine