Leucine tolerance in children with MSUD is not correlated with plasma leucine levels at diagnosis.

Objectives: Maple syrup urine disease (MSUD) is an inborn metabolic disease. The nutritional treatment with restricted intake of branched chain amino acids and prevention of leucine toxicity are crucially important for a favorable outcome. The aim of this study is to analyze the relation of blood leucine levels at diagnosis with future leucine tolerances, to determine whether any prediction about the future leucine tolerances or plasma leucine levels is possible by evaluating blood leucine levels at diagnosis.

Methods: The study group consisted of 45 MSUD patients. Leucine levels at diagnosis were compared with age at diagnosis, leucine tolerances, maximum leucine levels/ages, and average blood leucine levels.

Results: The mean plasma leucine level at diagnosis was 2,355.47 ± 1,251.7 μmol/L (ref: 55-164 μmol/L). The median age at diagnosis was 17 days. Leucine tolerances per kg body weight declined until the age of 8 years and stabilized subsequently. The average age of maximum leucine level during follow-up was 3.14 ± 1.92 years, and the mean maximum lifetime plasma leucine level on follow-up was 1,452.13 ± 621.38 μmol/L. The leucine levels at diagnosis did not have any significant relationship with lifetime leucine tolerances, maximum plasma leucine levels or mean plasma leucine levels.

Conclusions: The plasma leucine levels at diagnosis did not have a predictive value for later leucine tolerances or plasma leucine levels. The maximum lifetime leucine level is likely to happen within the first 3 years of life, underlining the importance of good metabolic control and compliance to dietary treatment at early ages.