Alternative sources of valine and isoleucine for prompt reduction of plasma leucine in maple syrup urine disease patients: A case series

In maple syrup urine disease (MSUD), leucine (Leu) accumulation, and its metabolites cause brain toxicity, and at diagnosis rapid plasma Leu reduction is essential. Valine (Val) and isoleucine (Iso) supplements are necessary to promote anabolism and enable prompt reduction of plasma Leu. Val/Iso supplements are unavailable in Iran, so an alternative source was necessary. An emergency protocol was developed using an unconventional source of Val and Iso to prompt reduction of high plasma Leu levels during an acute metabolic crisis to prevent brain encephalopathy and neurological sequelae. Five children with classical MSUD were referred aged 1–25 months, with a prolonged high plasma Leu of more than 1500 μmol/L and acute symptoms (irritability, poor feeding, and hypotonia). Initially, breast milk/regular infant formula was stopped. Val and Iso were given in calculated amounts from a Leu‐free formula containing Iso/Val (Xleu Maxamaid, Nutricia Ltd.) to promote anabolism. It was prescribed for a controlled and limited time with a branched chain amino acid (BCAA) free formula. Frequent amino acid monitoring was conducted. Natural protein was re‐added after normalizing plasma Leu. Plasma Leu declined by a median (range) of 1677 (1501–1852) μmol/L within 3–4 days of intervention. The median follow‐up time was 24 months (range: 14–32) and patients showed improvement in motor and cognitive skills after normalizing plasma Leu (75–200 μmol/L). Most had improvement in their head circumference (n = 4). Due to the unavailability of individual Val/Iso supplements, a Leu‐free formula rapidly lowered plasma Leu concentrations during acute crisis, to prevent cerebral edema and brain damage in MSUD.