PAF research summary Elango

PAF Awards $44,253 New Research Grant

Rajavel Elango, PhD, University of British Columbia

“Optimizing amino acids in medical foods to manage propionic acidemia”  

Propionic Acidemia (PA) is primarily caused by an enzymatic defect, propionyl-CoA carboxylase (PCC), in the catabolic pathway of valine, isoleucine and other propiogenic precursors. The dietary management of PA mainly depends on protein restriction from food to reduce supply of propiogenic amino acids, and the use of special medical foods. These medical foods contain all essential amino acids and nutrients, but no propiogenic compounds. Recently, concerns have been raised about their use, due to the imbalanced content of the Branched Chain Amino Acids (BCAA) – high leucine, to minimal or no valine and isoleucine. The imbalanced mixture of BCAA negatively impacts plasma concentrations of valine and isoleucine, and has been proposed to affect growth in pediatric PA patients. 

In an ongoing retrospective natural history study (n=4), patients with PA treated at our center from birth (or diagnosis) to age 18y, we observed that higher intake of medical food (compared to intact protein) results in lower ht-for-age Z scores. Based on these pilot data, we propose that there is an immediate need to determine the optimal amounts of leucine to be present in the medical foods.

Therefore, the specific objectives of the current study are to:

  1. Stable isotope studies
    1. Determine the ideal ratio among BCAA in children using the stable isotope-based indicator amino acid method to optimize protein synthesis in a Proof-of-Principle approach.
    2. Test the ratio among BCAA using the same stable isotope-based method in our cohort of PA patients to determine impact on protein synthesis, and plasma metabolite responses.
  2. Determine the impact of the use of natural (intact) vs formula (medical food) protein on anthropometric, biochemical and clinical outcomes via a retrospective natural history study of PA patients treated at BC Children’s Hospital.

Recent dietary guidelines for PA are discouraging the reliance on medical foods as a sole dietary source. However most individuals with PA are at risk for malnutrition and depend on these medical foods as an easy tolerable source of energy and protein. Thus, determining the optimal ratio of BCAA in PA medical foods is necessary to optimize protein synthesis, promote anabolism, growth and prevent the accumulation of toxic metabolites. 

Our laboratory, equipped with use of novel stable isotope tracers to examine protein and amino acid metabolism, is ideally suited to address the question of the ideal BCAA ratio to be used for dietary management of PA and potentially impact health outcomes.


The Propionic Acidemia Nutrition Guidelines are now published

Great News – The “Propionic Acidemia Nutrition Guidelines” Are Now Published!

The Nutrition Guideline Committee is happy to announce that the Organic Acidemia Workgroup has published the “Propionic Acidemia (PROP) Nutrition Guidelines” in the February, 2019 issue of Molecular Genetics and Metabolism. The article is available and can be downloaded at no cost at

Publication of the PROP/PA Nutrition Guidelines in Molecular Genetics and Metabolism brings the latest evidence- and consensus-based nutrition management recommendations to the attention of clinicians, researchers, policy makers, insurers, and patients.

The new Nutrition Management Guidelines for PROP/PA provide:

  • New directions including:
    • A greater emphasis on nutritional needs such as nutrient intake, nutritional interventions, supplementation, etc.
    • Less emphasis on  medical management which has been covered in previous publications;
    • Additional topics such as monitoring to ensure nutritional adequacy, nutritional issues with pregnancy and lactation, nutritional management for secondary complications such as pancreatitis, and finally a section addressing liver transplantation and the nutritional management before, during, and after the procedure.


Two consumer-oriented pieces, Frequently Asked Questions and a Consumer Summary, provide patients and families with information to use when interacting with their providers. The summary highlights key recommendations and suggests questions that patients and families may want to discuss with the metabolic team.

  • When patients and health care providers (HCPs) have the same information, they can work together as a team to identify the treatment that is best for the patient’s situation.
  • You can access these pieces at the Genetic Metabolic Dietitians International (GMDI) or Southeast Genetics Network websites located at  and
  • The new guidelines should lead to greater consistency of care across centers.
    • There are several important resources included in the guidelines including recommended nutrient intakes, monitoring schedules, and nutritional interventions tables.
    • A web site that provides all the resources and references used to develop the guidelines is available so that health care clinicians and others can readily obtain the background information related to the guidelines at the websites listed above.
    • The guidelines development method utilized evidence from published research, practice-based medical literature and expert consensus processes.