Management
Guidelines
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MSUD Nutrition Management Guidelines
First Edition
February 2013, v.1.58
Updated: June 2021
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Nutrition Recommendations
Question
2. For the individual with MSUD treated through dietary modification, what are BCAA blood levels that lead to optimal nutrition, medical and quality of life outcomes?
Conclusion Statement
Derived from evidence and consensus based clinical practice

Studies in this analysis have focused primarily on identifying plasma BCAA concentrations that result in adverse outcomes.  Elevated LEU levels are most often associated with abnormal brain morphology and cognitive impairment; impact on social and psychomotor function varies. Low plasma BCAA, particularly ILE and to a lesser extent VAL, results in severe but reversible epithelial damage to the skin, eye and gastrointestinal tract. Poor growth is reported as a result of BCAA deficiency. The goal of dietary BCAA restriction in the person with MSUD is to quickly achieve and maintain plasma BCAA concentrations as close to normal as possible while preventing and correcting BCAA deficiencies. However, reports differ in the plasma BCAA ranges that are considered acceptable but agree that biochemical monitoring is necessary to assess the effectiveness of dietary intervention. Although relaxing dietary BCAA restriction in adolescents and adults has been reported in case studies and postulated to improve quality of life, this practice poses a risk of adverse outcomes and has not been rigorously or objectively evaluated.

Recommendation 2.1

Maintain plasma LEU, with frequent monitoring, between 75-200 µmol/L for infants and children < 5 years of age and between 75-300 µmol/L for individuals >5 years of years of age to achieve favorable cognitive outcomes.

Strength of Recommendation:
Insufficient EvidenceConsensusWeakFairStrong
Clinical Action:
ConditionalImperative
Recommendation 2.2

Maintain plasma ILE and VAL concentrations between 200-400 µmol/L (or slightly above the normal ranges) in individuals with MSUD to avoid metabolic instability and BCAA deficiencies.

Strength of Recommendation:
Insufficient EvidenceConsensusWeakFairStrong
Clinical Action:
ConditionalImperative
Recommendation 2.3

Maintain plasma BCAA within the recommended ranges throughout life.

Strength of Recommendation:
Insufficient EvidenceConsensusWeakFairStrong
Clinical Action:
ConditionalImperative
Recommendation 2.4

Employ MSUD-specific dietary management strategies to achieve recommended BCAA levels. See TABLE #4, Recommended Dietary PRO, BCAA and Energy Intake.

Strength of Recommendation:
Insufficient EvidenceConsensusWeakFairStrong
Clinical Action:
ConditionalImperative
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