Cerebral edema (swelling of the brain) commonly occurs when a person with MSUD is in metabolic crisis. As cerebral edema has the potential to cause brain damage, prevention and effective treatment of cerebral edema is a major focus of clinicians. The precise mechanism by which high levels of leucine damage the brain are not known. This study used rats to look at the effect of branched-chain amino acids (BCAAs) on the brain, and examined the effect of dexamethasone, a steroid drug which has been found effective in treating cerebral edema resulting from brain tumors and other causes.

The authors demonstrated that elevated BCAA levels increase the permeability of the brain, allowing greater amounts of fluid and small molecules to enter. They also found that when rats were given dexamethasone, permeability of the brain, brain swelling and brain damage was reduced.