Propionyl CoA is an intermediate in the catabolism of the amino acids leucine (LEU), isoleucine (ILE), threonine (THR) and methionine (MET), and of odd chain fatty acids. When the pathway is blocked by the loss of catalytic activity of the enzyme propionyl CoA carboxylase, there is an accumulation of propionyl CoA. The propionyl CoA enters minor pathways to be converted to propionylcarnitine, propionyl glycine, 3-OH propionic acid and propionic acid. Propionic acid can disrupt the tricarboxylic acid cycle (TCA) by combining with oxaloacetate to form 2-methylcitrate.There is also inhibition of N-acetyl glutamate synthetase (NAGS) disrupting the urea cycle and causing hyperammonemia.

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The goals of medical nutrition therapy in PROP are to:

• Reduce toxic metabolite accumulation by restricting dietary sources of VAL, ILE, MET and THR while maintaining normal concentrations of plasma amino acids
• Avoid prolonged fasting to reduce production of odd chain fatty acids
• Reduce catabolism
• Promote anabolism
• Promote normal growth, development and health maintenance