Glutaryl-CoA dehydrogenase deficiency (GDD; McKusick 231670) orglutaric aciduria type I is an inborn error of lysine, hydroxylysineand tryptophan catabolism due to deficiency of glutaryl-CoAdehydrogenase (EC 1.3.99.7). The mitochondrial flavin-adeninedinucleotide-requiring enzyme catalyses the dehydrogenation ofglutaryl-CoA as well as the subsequent decarboxylation ofglutaconyl-CoA to crotonyl-CoA. Clinical and biochemicalcharacteristics of the disease, especially the course of disease, aredistinct and different from other well-known disorders of amino acidcatabolism (Amir et al 1989; Haworth et al 1991; Hoffmann et al 1991;Morton et al 1991; Kyllerman et al 1994).Following a workshop in 1993, new data not previously published arepresented in this report on more than 20 patients with GDD, revealinghitherto unreported details of the clinical presentation and thenatural history of this probably still widely underdiagnosedneurometabolic disorder.