Glutaric aciduria type 1: Genetic and phenotypic spectrum in 53 patients

Comprehensive metabolomics analysis reveals novel biomarkers and pathways in falsely suspected glutaric aciduria Type-1 newborns

BACKGROUND

Glutaric aciduria type-1 (GA-1) is a rare metabolic disorder due to glutaryl coenzyme A dehydrogenase deficiency, causing elevated levels of glutaryl-CoA and its derivatives. GA-1 exhibits symptoms like macrocephaly, developmental delays, and movement disorders. Timely diagnosis through genetic testing and newborn screening is crucial. However, in some cases, transiently elevated level of glutarylcarnitine (C5DC) challenges accurate diagnosis, highlighting the need for alternative diagnostic methods, like mass spectrometry-based untargeted metabolomics, to identify additional biomarkers for distinguishing falsely suspected GA-1 from healthy newborns.

METHODOLOGY

DBS samples from falsely suspected GA-1 newborns (n = 47) and matched control were collected through the NBS program. Untargeted metabolomics using liquid chromatography-high-resolution mass spectrometry (LC-HRMS) was performed to enable biomarker and pathway investigations for significantly altered metabolites.

RESULTS

582 and 546 were up- and down-regulated metabolites in transient GA-1. 155 endogenous metabolites displayed significant variations compared to the control group. Furthermore, our data identified novel altered metabolic biomarkers, such as N-palmitoylcysteine, heptacarboxyporphyrin, 3-hydroxylinoleoylcarnitine, and monoacylglyceride (MG) (0:0/20:1/0:0), along with perturbed metabolic pathways like sphingolipid and thiamine metabolism associated with the transient elevated C5DC levels in DBS samples.

CONCLUSIONS

A distinct metabolic pattern linked to the transient C5DC elevation in newborns was reported to enhance the prediction of the falsely positive cases, which could help avoiding unnecessary medical treatments and minimizing the financial burdens in the health sector.

Glutaric aciduria and L-2-hydroxyglutaric aciduria: Clinical and molecular findings of 35 patients from Turkey

Background

Cerebral organic acid disorders are progressive neurometabolic diseases characterized by neurologic dysfunction. Glutaric aciduria type I (GA-I) and L-2-hydroxyglutaric aciduria (L2HGA) are the main cerebral organic acid disorders. They are both classified as, and it is suggested that these two disorders may share a common metabolic pathway. Current treatment strategies are based on levocarnitine, vitamin B2, and diet. Recent guidelines recommend a lysine-restricted diet up to six years of age, but there is no consensus for patients over the age of six. Vitamin B2 is exists in the blood as riboflavin and its cofactors, flavin mononucleotide and flavin adenine dinucleotide (FAD). FAD, the cofactor of L2HGD, accelerates the conversion of L-2-hydoxy glutarate to alpha-ketoglutarate. Levocarnitine stimulates the formation and excretion of derivatives of glutaric acid. Also, lysine-associated organic acidurias some results provide principal proof for the beneficial effects of riboflavin in GA-I. It has been previously reported that combination therapy with riboflavin and levocarnitine is effective for L2HGA as well as GA-I. Riboflavin and levocarnitine have been reported to improve not only clinical symptoms but also urinary 2-HGA levels. In our study, we aimed to evaluate the effect of the current treatment strategies and genotype on urinary metabolites and IQ scores in GA-I and L2HGA patients.

Methods

The presented retrospective multicenter study included patients followed up in Diyarbakir Children's Hospital and Izmir Katip Celebi University Faculty of Medicine, Division of Pediatric Metabolism. Between 2016 and 2021, we retrospectively evaluated 35 patients with confirmed diagnosis of GA-I and L-2HGA. We analyzed the clinical, biochemical, neuroradiological, molecular data and treatment of the patients. The follow-up period was every 2 months until 12 months old, every 3 months until 6 years of age, and every 6 months thereafter. Therapy monitoring was undertaken during follow-up visits that included evaluation of clinical parameters, laboratory parameters, and dietary consumption records. Denver II was applied in order to evaluate children aged 0-6 years in terms of development. Patients between 6 and 16 years of age were evaluated using the Wechsler Intelligence Scale for Children-Revised.

Results

We identified 25 with GA-I and 10 with L2HGA. The most common clinical symptoms were developmental delay, intellectual disability, and movement disorders. Behavioural problems were more common in L2HGA than in GA-I patients. In the same family, there were patients with severe developmental delay despite early diagnosis and treatment and individuals with normal IQ scores. In our study group, we used diet (lysine restricted or protein controlled), levocarnitine and vitamin B2 for GA-I patients. The mean urinary glutaric acid levels were decreased with treatment in GA-I patients. Group I consisted of 14/25 patients receiving lysine restricted diet and levocarnitine, Group II (8/25) received protein-controlled diet and levocarnitine. Group III (3/25) patients whom had p.Pro248Leu (P248L) variant, received riboflavin in combination with protein-controlled diet and levocarnitine. When we evaluated according to the treatment groups, a significant decrease was observed in urinary glutaric acid levels in group I. But there were no significant difference in Group II and III. The patients with c.1018C > T variant in GCDH gene had higher pre-treatment urinary metabolites and significant reduction in urinary metabolites with treatment was detected. In L2HGA patients, we used levocarnitine and vitamin B2. In all L2HGA patients, there was a significant decrease in the mean urinary 2- hydoxy glutarate with treatment. However, there was no significant difference between the c.164G > A and c.1115delT variants. The mean pre- and post-treatment IQ scores of GA-I patients, no significant difference was observed. Relative neurologic improvement was seen in three L2HGA patients. We found two novel variants, including the c.221A > G (p.Tyr74Cys) in the GCDH gene and the c.738 + 5A > G splice variant in the L2HGDH gene.

Conclusions

Glutaric aciduria type I and L2HGA are the most common cerebral organic acidurias. Early and correct diagnosis is crucial. Poor prognosis based on metabolic crises and progressive deterioration still appears. In countries where newborn screening is not performed, a clinical suspicion index is required for cerebral organic aciduria. GA-I and L-2HGA are difficult to examine by medical evidence standards because of the small sample size, regional differences in newborn screening, and medical care limits. More clinical studies are needed to identify effective treatments. However, the significant decrease in urinary glutaric acid levels after treatment in patients on lysine-restricted diet raises the question of whether lysine-restricted diet should be continued after six years of age. We also reported our experience in order to contribute to the literature.

Update current understanding of neurometabolic disorders related to lysine metabolism

Lysine, as an essential amino acid, predominantly undergoes metabolic processes through the saccharopine pathway, whereas a smaller fraction follows the pipecolic acid pathway. Although the liver is considered the primary organ for lysine metabolism, it is worth noting that lysine catabolism also takes place in other tissues and organs throughout the body, including the brain. Enzyme deficiency caused by pathogenic variants in its metabolic pathway may lead to a series of neurometabolic diseases, among which glutaric aciduria type 1 and pyridoxine-dependent epilepsy have the most significant clinical manifestations. At present, through research, we have a deeper understanding of the multiple pathophysiological mechanisms related to these diseases, including intracerebral accumulation of neurotoxic metabolites, imbalance between GABAergic and glutamatergic neurotransmission, energy deprivation due to metabolites, and the dysfunction of antiquitin. Because of the complexity of these diseases, their clinical manifestations are also diverse. The early implementation of lysine-restricted diets and supplementation with arginine and carnitine has reported positive impacts on the neurodevelopmental outcomes of patients. Presently, there is more robust evidence supporting the effectiveness of these treatments in glutaric aciduria type 1 compared with pyridoxine-dependent epilepsy.

Evaluation of the Clinical, Biochemical, Neurological, and Genetic Presentations of Glutaric Aciduria Type 1 in Patients From China

Purpose

To characterize the phenotypic and genotypic variations associated with Glutaric aciduria type 1 (GA1) in Chinese patients.

Methods

We analyzed the clinical, neuroradiological, biochemical, and genetic information from 101 GA1 patients in mainland China.

Results

20 patients were diagnosed by newborn screening and the remaining 81 cases were identified following clinical intervention. Macrocephaly was the most common presentation, followed by movement disorders and seizures. A total of 59 patients were evaluated by brain MRI and 58 patients presented with abnormalities, with widening of the sylvian fissures being the most common symptom. The concentration of glutarylcarnitine in the blood, glutarylcarnitine/capryloylcarnitine ratio, and urine levels of glutaric acid were increased in GA1 patients and were shown to decrease following intervention. A total of 88 patient samples were available for genotyping and 74 variants within the GCDH gene, including 23 novel variants, were identified. The most common variant was c.1244-2A > C (18.4%) and there were no significant differences in the biochemical or clinical phenotypes described for patients with the four most common variants: c.1244-2A > C, c.1064G > A, c.533G > A, and c.1147C > T. Patients identified by newborn screening had better outcomes than clinical patients.

Conclusion

Our findings expand the spectrum of phenotypes and genotypes for GA1 in Chinese populations and suggest that an expanded newborn screening program using tandem mass spectrometry may facilitate the early diagnosis and treatment of this disease, improving clinical outcomes for patients in China.