GCDH and glutaryl-CoA dehydrogenase deficiency: In this paper we aimed to focus on glutaric aciduria type 1 phenotype, especially head MRI and circumference with relation to biochemical and genetic results (urinary excretion of glutaric and 3-hydroxyglutaric acids and causative pathogenic variants in GCDH gene, respectively) based on clinical data of 13 Polish patients.