3-Methylglutaconic aciduria type I redefined: a syndrome with late-onset leukoencephalopathy

3-Methylglutaconic aciduria type I is a rare inborn error of leucine catabolism. It is thought to present in childhood with nonspecific symptoms; it was even speculated to be a nondisease. The natural course of disease is unknown.

This is a study on 10 patients with 3-methylglutaconic aciduria type I. We present the clinical, neuroradiologic, biochemical, and genetic details on 2 new adult-onset patients and follow-up data on 2 patients from the literature.

Two unrelated patients with the characteristic biochemical findings of 3- methylglutaconic aciduria type I presented in adulthood with progressive ataxia. One patient additionally had optic atrophy, the other spasticity and dementia. Three novel mutations were found in conserved regions of the AUH gene. In both patients, MRI revealed extensive white matter disease. Follow-up MRI in a 10-year-old boy, who presented earlier with isolated febrile seizures, showed mild abnormalities in deep white matter.

We define 3-methylglutaconic aciduria type I as an inborn error of metabolism with slowly progressive leukoencephalopathy clinically presenting in adulthood. In contrast to the nonspecific findings in pediatric cases, the clinical and neuroradiologic pattern in adult patients is highly characteristic. White matter abnormalities may already develop in the first decades of life. The variable features found in affected children may be coincidental. Long-term follow-up in children is essential to learn more about the natural course of this presumably slowly progressive disease. Dietary treatment with leucine restriction may be considered.