Novel glycine conjugates in medium‐chain acyl‐CoA dehydrogenase deficiency

Summary The glycine conjugates of isocaproic, 4‐methylhexanoic, 7‐hydroxyoctanoic and 8‐hydroxyoctanoic acids have been identified in the urine of children with medium‐chain acyl‐CoA dehydrogenase (MCAD) deficiency using gas chromatography‐mass spectrometry of the trimethylsilyl derivatives. A quantitative study showed that the glycine conjugates of isocaproic and 4‐methylhexanoic acids were excreted during acute episodes and in smaller amounts when subjects were asymptomatic. The glycine conjugates of 7‐hydroxyoctanoic and 8‐hydroxyoctanoic acids were detectable during acute episodes. None of the conjugates was detected in controls or controls receiving a diet containing medium‐chain triglycerides. It is suggested that the glycine conjugates of isocaproic acid and 4‐methylhexanoic acid are metabolites of branched‐chain fatty acids and that they are specific for MCAD deficiency.