EFFECT OF MEDICAL FOODS USED IN DIETARY MANAGEMENT OF SUBJECTS WITH PROPIONIC ACIDEMIA (PROP)

Abstract

Introduction: Propionic Acidemia (PROP) is an inborn errors of metabolism disorder, caused by a defect in the enzyme propionyl-CoA carboxylase (PCC). PCC catalyzes two of the branched-chain amino acids (BCAA), valine, isoleucine. The management of PROP depends on dietary protein restriction and medical food consumption. Recently, concerns have been raised about medical foods due to imbalanced content of BCAA (high leucine – another BCAA, and no valine/isoleucine). It has been suggested that this imbalanced mixture of BCAA negatively impacts plasma concentrations of valine and isoleucine, and therefore growth in children with PROP. Studies on long-term growth outcomes in subjects with PROP are limited. Thus, a comprehensive assessment of dietary intake and its impact on growth in children with PROP is needed. Furthermore, since subjects with PROP depend on medical foods as an easily tolerable source of energy and protein, there is a need to determine the optimal BCAA ratio in medical foods to optimize protein synthesis and growth. Methods & Results: A retrospective chart review was conducted on four subjects with PROP; longitudinal data on dietary intake and growth outcomes for 1999-2018 were collected. Results suggest that subjects had persistently low height Z scores, despite consuming protein intakes higher than guidelines. However, the high consumption of medical foods protein relative to intact protein impacted growth. A prospective study to test different BCAA (LEU: ILE: VAL) ratios was conducted using the indicator amino acid oxidation method. Eight healthy children participated at 7 different test intakes with the use of L-1-13C-Phenylalanine oxidation to 13CO2 as a marker of protein synthesis. ANOVA showed significant differences with different test iv intakes, with a ratio between 1: 0.26: 0.28 and 1:0.35:0.4 observed to be associated with optimal protein synthesis. Conclusion: Our results indicate that intact protein restriction together with overusing medical foods could have affected growth in children with PROP. Currently used medical foods are formulated to provide an imbalanced BCAA (1:0:0), which was associated with the highest oxidation rates (indicating low protein synthesis). Future studies should examine the effect of BCAA ratios between (1:0.26:0.28) and (1:0.35:0.4) in subjects with PROP to measure adequacy for protein synthesis.