Phenotypic heterogeneity in two siblings with 3-methylglutaconic aciduria type I caused by a novel intragenic deletion

We describe two siblings with 3-methylglutaconic aciduria type I with phenotypic heterogeneity. The index case was a 14-year-old female with learning disability, attention deficit-hyperactivity and early onset subclinical leukoencephalopathy. Her 9-year-old brother had severe expressive speech delay and delay in speech sound development with normal cognitive functions. The diagnosis was confirmed by a demonstration of 3-methylglutaconyl-CoA hydratase enzyme deficiency in the cultured skin fibroblasts and homozygous deletion of exons 1–3 within the AUH gene.