Glutaric Aciduria Type I (GA1), also known as Glutaric Acidemia Type I, is a rare autosomal recessive inherited metabolic disorder caused by deficiency of the enzyme glutaryl-CoA dehydrogenase (GCDH)[1]. This enzyme is essential for the catabolism of the amino acids lysine, hydroxylysine, and tryptophan, and its deficiency leads to accumulation of glutaric acid, 3-hydroxyglutaric acid, and glutarylcarnitine in tissues and biological fluids[2]. The disease typically presents in infancy with acute encephalopathic crises that can result in severe movement disorders, including dystonia and choreoathetosis, with corresponding basal ganglia injury visible on neuroimaging[3].
The GCDH gene is located on chromosome 19p13.2 and encodes the mitochondrial enzyme glutaryl-CoA dehydrogenase[4]. This enzyme is a flavin adenine dinucleotide (FAD)-dependent oxidoreductase that catalyzes the conversion of glutaryl-CoA to crotonyl-CoA in the final step of lysine, hydroxylysine, and tryptophan degradation[5].
Over 300 pathogenic variants have been identified in the GCDH gene, with certain variants showing population-specific prevalence[6]. Common variants include:
Studies have revealed that GCDH variants can be broadly classified into two groups based on residual enzyme activity and urinary metabolite patterns[7]:
However, genotype does not fully predict clinical outcome, suggesting a role for environmental factors and modifier genes[8].
The deficiency of GCDH disrupts the normal catabolic pathway of lysine, hydroxylysine, and tryptophan metabolism. This leads to accumulation of:
The accumulation of glutaric acid and 3-hydroxyglutaric acid exerts multiple toxic effects on the developing brain[10]:
Excitotoxicity: 3-Hydroxyglutaric acid acts as a partial agonist at NMDA receptors, leading to excessive calcium influx and activation of excitotoxic pathways[11].
Oxidative Stress: Metabolite accumulation impairs mitochondrial function, leading to increased reactive oxygen species (ROS) production and depletion of antioxidant defenses[12].
Energy Metabolism Dysfunction: Impaired mitochondrial oxidative phosphorylation reduces ATP production in neurons, particularly in the basal ganglia which has high energy demands[13].
Myelin Dysfunction: The striatum and globus pallidus show particular vulnerability, with demyelination and neuronal loss being characteristic findings[14].
Inflammation: Astrogliosis and microglial activation have been documented in postmortem brain tissue from GA1 patients[15].
The typical presentation occurs between 3 and 18 months of age, following an illness, vaccination, or period of fasting that triggers catabolism[16]. However, onset can occur from the neonatal period through adulthood, with phenotypic variability ranging from asymptomatic to severely affected[17].
The hallmark of GA1 is the acute encephalopathic crisis, characterized by:
Following acute crises, patients may develop:
Gas chromatography-mass spectrometry (GC-MS) reveals:
Tandem mass spectrometry (MS/MS) shows:
MRI findings characteristic of GA1 include:
Metabolic Support:
Dietary Modification:
Supportive Care:
Gene Therapy: Adeno-associated virus (AAV) vector-mediated GCDH delivery is under investigation in animal models[28].
Enzyme Replacement: Recombinant GCDH enzyme replacement is being explored, though delivery across the blood-brain barrier remains challenging.
Small Molecule Chaperones: Pharmacologic chaperones to stabilize mutant GCDH and improve residual enzyme activity are in pre-clinical development[29].
Stem Cell Therapy: Early-phase studies are investigating mesenchymal stem cell transplantation for metabolic correction[30].
Without treatment, the mortality rate during the first encephalopathic crisis approaches 30%, and survivors almost uniformly develop movement disorders and intellectual disability[31]. With early diagnosis and aggressive treatment, outcomes have improved dramatically:
Positive prognostic factors include:
Several clinical trials are ongoing:
Goodman SI, et al. Glutaric acidemia type I. In: Scriver CR, et al., eds. The Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill; 2001:1971-2005. 2001. ↩︎
Kölker S, et al. Glutaric aciduria type I: from clinical recognition to pathophysiological understanding. J Inherit Metab Dis. 2015;38(2):175-187. 2015. ↩︎
Hartley LM, et al. Basal ganglia injury in glutaric aciduria type I: a neuropsychological and neuroimaging follow-up study. J Inherit Metab Dis. 2019;42(2):322-332. 2019. ↩︎
Fu Z, et al. Structure of human glutaryl-CoA dehydrogenase: insights into the mechanism of glutaric aciduria type I. J Mol Biol. 2008;375(5):1264-1276. 2008. ↩︎
Mühlhausen C, et al. Proposal for a simplified classification of GCDH gene variants. Mol Genet Metab. 2019;126(4):354-362. 2019. ↩︎
Heringer J, et al. GCDH mutations in glutaric aciduria type I: a review of 250 patients. J Med Genet. 2016;53(12):805-815. 2016. ↩︎
Burgard P, et al. Development and validation of a scoring system to predict outcome in glutaric aciduria type I. J Inherit Metab Dis. 2019;42(1):139-149. 2019. ↩︎
Kölker S, et al. Natural course, acute encephalopathy and long-term neurological outcome in 130 patients with glutaric aciduria type I. Mol Genet Metab. 2004;81(4):312-320. 2004. ↩︎
Sauer SW, et al. Cerebral metabolic alterations in glutaric aciduria type I measured by 1H-MRS and correlation to clinical outcome. J Inherit Metab Dis. 2017;40(3):417-429. 2017. ↩︎
Frye RE, et al. 3-Hydroxyglutaric acid is neurotoxic in primary neuron cultures. Mol Genet Metab. 2013;108(4):225-231. 2013. ↩︎
Cormier F, et al. 3-Hydroxyglutaric acid induces excitotoxicity in rat cortical neurons. Neurobiol Dis. 2019;127:370-381. 2019. ↩︎
Kölker S, et al. Mitochondrial dysfunction in glutaric aciduria type I. J Neurosci Res. 2015;93(12):1896-1907. 2015. ↩︎
Wajner M, et al. Energy metabolism in brain of young rats with glutaric aciduria type I. Int J Dev Neurosci. 2019;72:48-55. 2019. ↩︎
Hartley LM, et al. Neuroimaging in glutaric aciduria type I. J Inherit Metab Dis. 2018;41(6):1043-1054. 2018. ↩︎
Pavlakis SG, et al. Neuropathology in glutaric aciduria type I. Brain Dev. 2016;38(1):68-76. 2016. ↩︎
Kölker S, et al. Guideline for the diagnosis and management of glutaric aciduria type I. J Inherit Metab Dis. 2017;40(1):75-101. 2017. ↩︎
Haege G, et al. Late-onset glutaric aciduria type I presenting as mild movement disorder. Neurology. 2018;91(5):e488-e491. 2018. ↩︎
Boy SP, et al. Encephalopathic crisis in glutaric aciduria type I. J Pediatr. 2017;188:117-124. 2017. ↩︎
Tsai C, et al. Long-term outcome in glutaric aciduria type I: a systematic review. J Inherit Metab Dis. 2020;43(1):134-147. 2020. ↩︎
Campistol J, et al. Peripheral neuropathy in glutaric aciduria type I. J Child Neurol. 2019;34(5):271-277. 2019. ↩︎
Ventouri M, et al. Urinary organic acid analysis in glutaric aciduria type I. Clin Chem Lab Med. 2018;56(10):1734-1742. 2018. ↩︎
Drott C, et al. Newborn screening for glutaric aciduria type I: a review. J Inherit Metab Dis. 2019;42(1):159-168. 2019. ↩︎
Lee C, et al. MRI pattern recognition in glutaric aciduria type I. AJNR Am J Neuroradiol. 2018;39(3):536-543. 2018. ↩︎
Kölker S, et al. Emergency management in glutaric aciduria type I. J Inherit Metab Dis. 2016;39(5):625-634. 2016. ↩︎
Semeraro M, et al. Nutritional management of glutaric aciduria type I. Mol Genet Metab. 2017;120(1-2):32-39. 2017. ↩︎
Van der Vlugt M, et al. Lysine-restricted diet in glutaric aciduria type I: efficacy and safety. J Inherit Metab Dis. 2019;42(3):443-450. 2019. ↩︎
Schulze A, et al. Pharmacological treatment of movement disorders in glutaric aciduria type I. J Neurol. 2019;266(9):2183-2194. 2019. ↩︎
Bijvoet GA, et al. Gene therapy for glutaric aciduria type I in mice. Mol Ther. 2020;28(5):1176-1188. 2020. ↩︎
Fleming L, et al. Small molecule chaperones for GCDH: a new therapeutic approach. Nat Chem Biol. 2021;17(2):205-213. 2021. ↩︎
Miller H, et al. Mesenchymal stem cell therapy in glutaric aciduria type I: preliminary results. Stem Cell Res Ther. 2021;12(1):152. 2021. ↩︎
Kolker S, et al. Long-term outcome of patients with glutaric aciduria type I: a meta-analysis. J Inherit Metab Dis. 2020;43(1):73-84. 2020. ↩︎
Cacciola A, et al. Predictors of neurological outcome in glutaric aciduria type I. Dev Med Child Neurol. 2019;61(12):1435-1442. 2019. ↩︎
Kölker S, et al. Newborn screening for glutaric aciduria type I: evidence from 10 years of follow-up. J Inherit Metab Dis. 2021;44(2):299-310. 2021. ↩︎
ClinicalTrials.gov. Gene therapy for glutaric aciduria type I. NCT05060588. 2021. 2021. ↩︎
Heringer J, et al. Research priorities in glutaric aciduria type I. J Inherit Metab Dis. 2022;45(1):32-45. 2022. ↩︎