Improved assay of glutaryl-CoA dehydrogenase in cultured cells and liver: application to glutaric aciduria type I

Abstract

Glutaric aciduria type I due to glutaryl-CoA dehydrogenase deficiency was first described by Goodman et al in 1975 [l]. Since then a number of cases with this neurological disorder has been reported [2-41. Glutaric acid is also excreted together with a variety of other organic acids in a syndrome called glutaric aciduria type II [5,6]. In this syndrome glutaryl-CoA dehydrogenase activity is normal [6]. Substantial excretion of glutaric acid can also accompany propionic acid and its metabolites in propionyl-CoA carboxylase deficiency [7]. In dicarboxylic acidurias of various types the excretion of glutaric acid can also be elevated [8]. In glutaric aciduria type I the urinary excretion of glutaric acid is usually accompanied by 3-OH-glutaric acid. This is useful in the differential diagnosis of glutaryl-CoA dehydrogenase deficiency. Although the clinical symptoms and glutaric aciduria in most cases suffice in the diagnosis of glutaryl-CoA dehydrogenase deficiency, glutaryl-CoA dehydrogenase determination is essential in other cases. The clinical symptoms can be quite variable and in some patients there is no excretion of 3-OH-glutaric acid [9]. For prenatal diagnosis of glutaric aciduria type I a sensitive and reliable assay for glutaryl-CoA dehydrogenase is a necessity, although increased concentration of glutaric acid has been found in the amniotic fluid from an affected fetus [lo]. Occasionally the diagnosis of glutaric aciduria type I has to be established after the death of a patient when only a urine specimen and a frozen liver sample are available. A reliable assay for glutaryl-CoA dehydrogenase in liver tissue is a prerequisite for a final diagnosis in such a case [9]. In this report we describe a refinement of an assay for glutaryl-CoA dehydrogenase in amniotic fluid cells and cultured fibroblasts suitable for the preand postnatal diagnosis of glutaric aciduria type I. Methods for the determination of the same enzyme in crude liver homogenate from autopsy and biopsy specimens are also reported.