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.

Recommendations for diagnosing and managing individuals with glutaric aciduria type 1: Third revision.

Glutaric aciduria type 1 is a rare inherited neurometabolic disorder of lysine metabolism caused by pathogenic gene variations in GCDH (cytogenic location: 19p13.13), resulting in deficiency of mitochondrial glutaryl-CoA dehydrogenase (GCDH) and, consequently, accumulation of glutaric acid, 3-hydroxyglutaric acid, glutaconic acid and glutarylcarnitine detectable by gas chromatography/mass spectrometry (organic acids) and tandem mass spectrometry (acylcarnitines). Depending on residual GCDH activity, biochemical high and low excreting phenotypes have been defined. Most untreated individuals present with acute onset of striatal damage before age 3 (to 6) years, precipitated by infectious diseases, fever or surgery, resulting in irreversible, mostly dystonic movement disorder with limited life expectancy. In some patients, striatal damage develops insidiously. In recent years, the clinical phenotype has been extended by the finding of extrastriatal abnormalities and cognitive dysfunction, preferably in the high excreter group, as well as chronic kidney failure. Newborn screening is the prerequisite for pre-symptomatic start of metabolic treatment with low lysine diet, carnitine supplementation and intensified emergency treatment during catabolic episodes, which, in combination, have substantially improved neurologic outcome. In contrast, start of treatment after onset of symptoms cannot reverse existing motor dysfunction caused by striatal damage. Dietary treatment can be relaxed after the vulnerable period for striatal damage, that is, age 6 years. However, impact of dietary relaxation on long-term outcomes is still unclear. This third revision of evidence-based recommendations aims to re-evaluate previous recommendations (Boy et al., J Inherit Metab Dis, 2017;40(1):75-101; Kolker et al., J Inherit Metab Dis 2011;34(3):677-694; Kolker et al., J Inherit Metab Dis, 2007;30(1):5-22) and to implement new research findings on the evolving phenotypic diversity as well as the impact of non-interventional variables and treatment quality on clinical outcomes.

[Expert consensus for the diagnosis and treatment of glutaricacidemia type 1].

Glutaricacidemia type 1(GA1) is an autosomal recessive disease caused by reduced or missing glutaryl-CoA dehydrogenase activity which hamps metabolism of lysine, hydroxylysine and tryptophan. The catabolic products of glutarylcarnitine and glutaric acid are abnormally accumulated in the body, resulting in metabolic disorders which primarily lead to damage to the nervous system. Clinical manifestations of patients include macrocephaly, dystonia, dyskinesia, and developmental retardation. Acute encephalopathy may be induced in infants and young children due to infection, vaccination and surgery. For GA1 is a rare disease and its clinical manifestations are similar to other neurological diseases, it may be easily missed or misdiagnosed. To facilitate early diagnosis and treatment and improve the prognosis, this consensus was formulated by pediatric experts from the fields of endocrinology and genetic metabolism through full discussion and reference to the latest literature and guidelines home and abroad.

Impact of newborn screening and quality of therapy on the neurological outcome in glutaric aciduria type 1: a meta-analysis.

PURPOSE: Glutaric aciduria type 1 (GA1), a rare inherited neurometabolic disorder, results in a complex movement disorder (MD) with predominant dystonia if untreated. Implementation into newborn screening (NBS) programs and adherence to recommended therapy are thought to improve the neurological outcome. METHODS: Systematic literature search for articles published from 2000 to 2019 was performed using the PRISMA protocol. Studies reporting on more than one individual identified by NBS were included. We investigated effects of interventional and noninterventional variables on neurological outcome. RESULTS: Fifteen publications reporting on 647 GA1 patients were included. In the NBS group (n = 261 patients), 195 patients remained asymptomatic (74.7%), while 66 patients (25.3%) developed a MD. Compared with the NBS group, a much higher proportion of patients (349/386; 90.4%; p < 0.0001) diagnosed after the manifestation of neurologic symptoms had a MD and an abnormal motor development (285/349; 81.7%; p < 0.0001). For NBS patients, deviations from the recommended diet increased the risk of insidious onset MD, while delayed start of emergency treatment increased the risk of acute onset MD. CONCLUSIONS: This meta-analysis demonstrates that NBS programs for GA1 have an overall positive effect on the neurological outcome of affected individuals but their success critically depends on the quality of therapy.

Impact of interventional and non-interventional variables on anthropometric long-term development in glutaric aciduria type 1: A national prospective multi-centre study.

Glutaric aciduria type 1 (GA1) is a rare neurometabolic disorder, caused by inherited deficiency of glutaryl-CoA dehydrogenase, mostly affecting the brain. Early identification by newborn screening (NBS) significantly improves neurologic outcome. It has remained unclear whether recommended therapy, particular low lysine diet, is safe or negatively affects anthropometric long-term outcome. This national prospective, observational, multi-centre study included 79 patients identified by NBS and investigated effects of interventional and non-interventional parameters on body weight, body length, body mass index (BMI) and head circumference as well as neurological parameters. Adherence to recommended maintenance and emergency treatment (ET) had a positive impact on neurologic outcome and allowed normal anthropometric development until adulthood. In contrast, non-adherence to ET, resulting in increased risk of dystonia, had a negative impact on body weight (mean SDS -1.07; P = .023) and body length (mean SDS -1.34; P = -.016). Consistently, longitudinal analysis showed a negative influence of severe dystonia on weight and length development over time (P < .001). Macrocephaly was more often found in female (mean SDS 0.56) than in male patients (mean SDS -0.20; P = .049), and also in individuals with high excreter phenotype (mean SDS 0.44) compared to low excreter patients (mean SDS -0.68; P = .016). In GA1, recommended long-term treatment is effective and allows for normal anthropometric long-term development up to adolescence, with gender- and excreter type-specific variations. Delayed ET and severe movement disorder result in poor anthropometric outcome.

Long-term survival of a patient with acute neonatal-onset metabolic encephalopathy with carbamoyl phosphate synthetase 1 deficiency.

OBJECTIVE: Long-term survival of patients with neonatal-onset carbamoyl-phosphate synthetase 1 deficiency (CPS1D), an autosomal recessive disorder characterized by repeated, life-threatening hyperammonemia, is rare. We describe the diagnosis and clinical management of a teenager with neonatal-onset CPS1D who did not undergo therapeutic liver transplantation. CASE REPORT: Following emergent neonatal therapy, the patient was diagnosed with CPS1D based on clinical, radiological, biochemical and genetic analyses. Her clinical course, neurobehavioral development and therapeutic interventions are presented and discussed. RESULTS: Born from nonconsanguineous parents, the proband underwent phototherapy for neonatal jaundice, associated with acute encephalopathy, apnea and cerebral edema. Based on blood and urinary biochemical abnormalities, neonatal-onset CPS1D was diagnosed. Her hyperammonemia was corrected by hemodialysis, followed by sodium benzoate, L-arginine, levocarnitine and protein-free diet therapy. Because of a relapse and persistent neurobehavioral regression by age 1, a planned liver transplantation was cancelled. At age 10, sodium phenylbutyrate was substituted as ammonia scavenger. Genetic testing revealed compound heterozygote c.2359C>T (R787X) and c.236+6T>C variants of CPS1, confirming her diagnosis. Despite severe neurological sequelae, the patient is 16 and in stable condition. CONCLUSIONS: Our case suggests that early hemodialysis and pharmacologic interventions for acute neonatal hyperammonemia can improve the prognosis of patients with neonatal-onset CPS1D.

Inherited Disorders of Lysine Metabolism: A Review.

Lysine is an essential amino acid, and inherited diseases of its metabolism therefore represent defects of lysine catabolism. Although some of these enzyme defects are not well described yet, glutaric aciduria type I (GA1) and antiquitin (2-aminoadipic-6-semialdehyde dehydrogenase) deficiency represent the most well-characterized diseases. GA1 is an autosomal recessive disorder due to a deficiency of glutaryl-CoA dehydrogenase. Untreated patients exhibit early onset macrocephaly and may present a neurological deterioration with regression and movement disorder at the time of a presumably "benign" infection most often during the first year of life. This is associated with a characteristic neuroimaging pattern with frontotemporal atrophy and striatal injuries. Diagnosis relies on the identification of glutaric and 3-hydroxyglutaric acid in urine along with plasma glutarylcarnitine. Treatment consists of a low-lysine diet aiming at reducing the putatively neurotoxic glutaric and 3-hydroxyglutaric acids. Additional therapeutic measures include administration of l-carnitine associated with emergency measures at the time of intercurrent illnesses aiming at preventing brain injury. Early treated (ideally through newborn screening) patients exhibit a favorable long-term neurocognitive outcome, whereas late-treated or untreated patients may present severe neurocognitive irreversible disabilities. Antiquitin deficiency is the most common form of pyridoxine-dependent epilepsy. α-Aminoadipic acid semialdehyde (AASA) and Δ-1-piperideine-6-carboxylate (P6C) accumulate proximal to the enzymatic block. P6C forms a complex with pyridoxal phosphate (PLP), a key vitamer of pyridoxine, thereby reducing PLP bioavailability and subsequently causing epilepsy. Urinary AASA is a biomarker of antiquitin deficiency. Despite seizure control, only 25% of the pyridoxine-treated patients show normal neurodevelopment. Low-lysine diet and arginine supplementation are proposed in some patients with decrease of AASA, but the impact on neurodevelopment is unclear. In summary, GA1 and antiquitin deficiency are the 2 main human defects of lysine catabolism. Both include neurological impairment. Lysine dietary restriction is a key therapy for GA1, whereas its benefits in antiquitin deficiency appear less clear.

The Evolution of Gene Therapy in the Treatment of Metabolic Liver Diseases.

Monogenic metabolic disorders of hepatic origin number in the hundreds, and for many, liver transplantation remains the only cure. Liver-targeted gene therapy is an attractive treatment modality for many of these conditions, and there have been significant advances at both the preclinical and clinical stages. Viral vectors, including retroviruses, lentiviruses, adenovirus-based vectors, adeno-associated viruses and simian virus 40, have differing safety, efficacy and immunogenic profiles, and several of these have been used in clinical trials with variable success. In this review, we profile viral vectors and non-viral vectors, together with various payloads, including emerging therapies based on RNA, that are entering clinical trials. Genome editing technologies are explored, from earlier to more recent novel approaches that are more efficient, specific and safe in reaching their target sites. The various curative approaches for the multitude of monogenic hepatic metabolic disorders currently at the clinical development stage portend a favorable outlook for this class of genetic disorders.

Deletion of 2-aminoadipic semialdehyde synthase limits metabolite accumulation in cell and mouse models for glutaric aciduria type 1.

Glutaric aciduria type 1 (GA1) is an inborn error of lysine degradation characterized by acute encephalopathy that is caused by toxic accumulation of lysine degradation intermediates. We investigated the efficacy of substrate reduction through inhibition of 2-aminoadipic semialdehyde synthase (AASS), an enzyme upstream of the defective glutaryl-CoA dehydrogenase (GCDH), in a cell line and mouse model of GA1. We show that loss of AASS function in GCDH-deficient HEK-293 cells leads to an approximately fivefold reduction in the established GA1 clinical biomarker glutarylcarnitine. In the GA1 mouse model, deletion of Aass leads to a 4.3-, 3.8-, and 3.2-fold decrease in the glutaric acid levels in urine, brain, and liver, respectively. Parallel decreases were observed in urine and brain 3-hydroxyglutaric acid levels, and plasma, urine, and brain glutarylcarnitine levels. These in vivo data demonstrate that the saccharopine pathway is the main source of glutaric acid production in the brain and periphery of a mouse model for GA1, and support the notion that pharmacological inhibition of AASS may represent an attractive strategy to treat GA1.

What are the information needs of parents caring for a child with Glutaric aciduria type 1?

BACKGROUND: Newborn screening has enabled the early diagnosis of Glutaric aciduria type 1, with the possibility of improving neurological outcomes in affected children. Achieving those outcomes requires parents to effectively manage their child's condition by adherence to a strict dietary regime and responding to situations that may trigger decompensation. The specific information and support needs of this group of parents are unknown. METHODS: A focus group with five parents was conducted to gain insights into the information that parents needed and the ways in which they accessed and used information to manage their child's condition. A topic guide was used to direct the discussion which was recorded and fully transcribed. All participants gave informed consent. Data were analysed using thematic analysis, a structured approach that contributes to transparency and validity of results while allowing the integration of predetermined and emerging themes. To ensure rigour, two researchers were involved in initial coding of data and key analytic decisions. RESULTS: Two main themes were identified. 'Understanding the condition' explored parent's needs to understand the scientific complexity of the condition and to be aware of the worst case scenario associated with loss of metabolic control. 'Managing the condition' explained how parents co-ordinated and controlled the involvement of other carers and parents' need to be active partners in medical management to feel in control of the situation. CONCLUSIONS: The study highlights the importance of addressing parents' initial and ongoing informational needs so they can fulfil their role and protect their child from metabolic harm.

Movement Disorders in Treatable Inborn Errors of Metabolism.

There are several hundred single-gene disorders that we classify as inborn errors of metabolism. Inborn errors of metabolism are often rare and highly heterogeneous multisystem diseases with non-neurological and neurological manifestations, commonly with onset during childhood. Movement disorders are among the most common neurological problems in inborn errors of metabolism, but, in many cases, remain poorly defined. Although movement disorders are usually not the only and often not the presenting symptom, their recognition can facilitate a diagnosis. Movement disorders contribute substantially to the morbidity in inborn errors of metabolism and can have a significant impact on quality of life. Common metabolic movement disorders include the monoamine neurotransmitter disorders, disorders of amino and organic acid metabolism, metal storage disorders, lysosomal storage disorders, congenital disorders of autophagy, disorders of creatine metabolism, vitamin-responsive disorders, and disorders of energy metabolism. Importantly, disease-modifying therapies exist for a number of inborn errors of metabolism, and early recognition and treatment can prevent irreversible CNS damage and reduce morbidity and mortality. A phenomenology-based approach, based on the predominant movement disorder, can facilitate a differential diagnosis and can guide biochemical, molecular, and imaging testing. The complexity of metabolic movement disorders demands an interdisciplinary approach and close collaboration of pediatric neurologists, neurologists, geneticists, and experts in metabolism. In this review, we develop a general framework for a phenomenology-based approach to movement disorders in inborn errors of metabolism and discuss an approach to identifying the "top ten" of treatable inborn errors of metabolism that present with movement disorders-diagnoses that should never be missed. © 2018 International Parkinson and Movement Disorder Society.

Newborn screening: A disease-changing intervention for glutaric aciduria type 1.

OBJECTIVE: Untreated individuals with glutaric aciduria type 1 (GA1) commonly present with a complex, predominantly dystonic movement disorder (MD) following acute or insidious onset striatal damage. Implementation of GA1 into newborn screening (NBS) programs has improved the short-term outcome. It remains unclear, however, whether NBS changes the long-term outcome and which variables are predictive. METHODS: This prospective, observational, multicenter study includes 87 patients identified by NBS, 4 patients missed by NBS, and 3 women with GA1 identified by positive NBS results of their unaffected children. RESULTS: The study population comprises 98.3% of individuals with GA1 identified by NBS in Germany during 1999-2016. Overall, cumulative sensitivity of NBS is 95.6%, but it is lower (84%) for patients with low excreter phenotype. The neurologic outcome of patients missed by NBS is as poor as in the pre-NBS era, and the clinical phenotype of diagnosed patients depends on the quality of therapeutic interventions rather than noninterventional variables. Presymptomatic start of treatment according to current guideline recommendations clearly improves the neurologic outcome (MD: 7% of patients), whereas delayed emergency treatment results in acute onset MD (100%), and deviations from maintenance treatment increase the risk of insidious onset MD (50%). Independent of the neurologic phenotype, kidney function tends to decline with age, a nonneurologic manifestation not predicted by any variable included in this study. INTERPRETATION: NBS is a beneficial, disease-changing intervention for GA1. However, improved neurologic outcome critically depends on adherence to recommended therapy, whereas kidney dysfunction does not appear to be impacted by recommended therapy. Ann Neurol 2018;83:970-979.

Treatment, Therapy and Management of Metabolic Epilepsy: A Systematic Review.

Metabolic epilepsy is a metabolic abnormality which is associated with an increased risk of epilepsy development in affected individuals. Commonly used antiepileptic drugs are typically ineffective against metabolic epilepsy as they do not address its root cause. Presently, there is no review available which summarizes all the treatment options for metabolic epilepsy. Thus, we systematically reviewed literature which reported on the treatment, therapy and management of metabolic epilepsy from four databases, namely PubMed, Springer, Scopus and ScienceDirect. After applying our inclusion and exclusion criteria as per the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, we reviewed a total of 43 articles. Based on the reviewed articles, we summarized the methods used for the treatment, therapy and management of metabolic epilepsy. These methods were tailored to address the root causes of the metabolic disturbances rather than targeting the epilepsy phenotype alone. Diet modification and dietary supplementation, alone or in combination with antiepileptic drugs, are used in tackling the different types of metabolic epilepsy. Identification, treatment, therapy and management of the underlying metabolic derangements can improve behavior, cognitive function and reduce seizure frequency and/or severity in patients.

Early neonatal Glutaric aciduria type I hidden by perinatal asphyxia: a case report.

BACKGROUND: Perinatal asphyxia (PA) occurs in about 2 to 10 per 1000 live full-term births. Although neonatal epileptic seizures are observed in up to 60% of cases, PA may mimic or subtend other conditions. Hypoxia related brain injury is particularly relevant, as it may have permanent effects on neuropsychomotor development. Antepartum obstetric conditions, may, in turn, lead to hypoxic-ischemic damage to the fetus and the newborn, often underlying PA. Herein, a case of PA that hid and triggered signs and symptoms of Glutaric Aciduria type I (GA-I), is reported. CASE PRESENTATION: R.F. was born at term after prolonged labour, by induced vaginal delivery with the Kristeller manoeuvre. He presented with severe asphyxia and asystoly. Immediate cardiopulmonary resuscitation promptly restored cardiorespiratory parameters, allowing for early extubation 30 min after. During the following hours, severe axial muscle hypotonia with an increased tone of the limb extensor muscles became evident. The absence of crying and archaic reflexes persisted and there was an onset of generalized tonic or clonic seizure. First level metabolic and inflammatory markers were within the normal range. An inherited metabolic disease was then suspected, due to the persistent clinical signs of severe neurological damage without any detectable septic parameter. GA-I was assessed and specific treatment started without any clinical improvement, although ensuring adequate growth and metabolic control. Thereafter, the baby developed a severe encephalopathy with drug resistant epileptic seizures. The progression of the neurological damage and a CVC-related sepsis led him to exitus at 2 years. CONCLUSIONS: To the best of our knowledge, this is the first case of early post-natal onset of GA-I reported in literature to date, in the absence of expanded newborn screening (NBS) programme. As expanded NBS programmes for inborn errors of metabolism have not yet been internationally adopted, we are of the opinion that such diseases may well be hidden by misleading signs and symptoms imputable to other more frequent harmful clinical conditions. Moreover, it would be advisable that neonatologists be trained to include GA-I in the differential diagnosis of neurological damage secondary to PA.

[Effect of glutaryl-CoA dehydrogenase gene silencing and high-concentration lysine on the viability of BRL hepatocytes].

OBJECTIVE: To investigate the effect of glutaryl-CoA dehydrogenase (GCDH) gene silencing and accumulation of lysine metabolites on the viability of hepatocytes. METHODS: BRL cells were divided into normal control group, negative control group, and GCDH silencing group. The shRNA lentiviral vector for silencing GCDH gene was constructed, and the BRL hepatocytes in the GCDH silencing group and the negative control group were infected with this lentivirus and negative control virus respectively, and then cultured in a medium containing 5 mmol/L lysine. Immunofluorescence assay was used to measure the infection efficiency of lentivirus. Western blot was used to measure the expression of GCDH protein. MTT assay was used to evaluate cell viability. Hoechest33342 staining was used to measure cell apoptosis. Western blot was used to measure the expression of Caspase-3, an index of cell apoptosis. RESULTS: The lentivirus constructed effectively silenced the GCDH gene in hepatocytes (P<0.01). MTT assay and Hoechest 33342 staining showed no significant differences in cell viability and apoptosis between groups (P>0.05). There was also no significant difference in the expression of Caspase-3 protein between groups (P>0.05). CONCLUSIONS: GCDH gene silencing and accumulation of lysine metabolites may not cause marked hepatocyte injury.

Treatment of Hyponatremic Encephalopathy in the Critically Ill.

OBJECTIVES: Hyponatremic encephalopathy, symptomatic cerebral edema due to a low osmolar state, is a medical emergency and often encountered in the ICU setting. This article provides a critical appraisal and review of the literature on identification of high-risk patients and the treatment of this life-threatening disorder. DATA SOURCES, STUDY SELECTION, AND DATA EXTRACTION: Online search of the PubMed database and manual review of articles involving risk factors for hyponatremic encephalopathy and treatment of hyponatremic encephalopathy in critical illness. DATA SYNTHESIS: Hyponatremic encephalopathy is a frequently encountered problem in the ICU. Prompt recognition of hyponatremic encephalopathy and early treatment with hypertonic saline are critical for successful outcomes. Manifestations are varied, depending on the extent of CNS's adaptation to the hypoosmolar state. The absolute change in serum sodium alone is a poor predictor of clinical symptoms. However, certain patient specific risks factors are predictive of a poor outcome and are important to identify. Gender (premenopausal and postmenopausal females), age (prepubertal children), and the presence of hypoxia are the three main clinical risk factors and are more predictive of poor outcomes than the rate of development of hyponatremia or the absolute decrease in the serum sodium. CONCLUSIONS: In patients with hyponatremic encephalopathy exhibiting neurologic manifestations, a bolus of 100 mL of 3% saline, given over 10 minutes, should be promptly administered. The goal of this initial bolus is to quickly treat cerebral edema. If signs persist, the bolus should be repeated in order to achieve clinical remission. However, the total change in serum sodium should not exceed 5 mEq/L in the initial 1-2 hours and 15-20 mEq/L in the first 48 hours of treatment. It has recently been demonstrated in a prospective fashion that 500 mL of 3% saline at an infusion rate of 100 mL per hour can be given safely. It is critical to recognize the early signs of cerebral edema (nausea, vomiting, and headache) and intervene with IV 3% sodium chloride as this is the time to intervene rather than waiting until more severe symptoms develop. Cerebral demyelination is a rare complication of overly rapid correction of hyponatremia. The principal risk factors for cerebral demyelination are correction of the serum sodium more than 25 mEq/L in the first 48 hours of therapy, correction past the point of 140 mEq/L, chronic liver disease, and hypoxic/anoxic episode.

Elevated glutaric acid levels in Dhtkd1-/Gcdh- double knockout mice challenge our current understanding of lysine metabolism.

Glutaric aciduria type I (GA-I) is a rare organic aciduria caused by the autosomal recessive inherited deficiency of glutaryl-CoA dehydrogenase (GCDH). GCDH deficiency leads to disruption of l-lysine degradation with characteristic accumulation of glutarylcarnitine and neurotoxic glutaric acid (GA), glutaryl-CoA, 3-hydroxyglutaric acid (3-OHGA). DHTKD1 acts upstream of GCDH, and its deficiency leads to none or often mild clinical phenotype in humans, 2-aminoadipic 2-oxoadipic aciduria. We hypothesized that inhibition of DHTKD1 may prevent the accumulation of neurotoxic dicarboxylic metabolites suggesting DHTKD1 inhibition as a possible treatment strategy for GA-I. In order to validate this hypothesis we took advantage of an existing GA-I (Gcdh-/-) mouse model and established a Dhtkd1 deficient mouse model. Both models reproduced the biochemical and clinical phenotype observed in patients. Under challenging conditions of a high lysine diet, only Gcdh-/- mice but not Dhtkd1-/- mice developed clinical symptoms such as lethargic behaviour and weight loss. However, the genetic Dhtkd1 inhibition in Dhtkd1-/-/Gcdh-/- mice could not rescue the GA-I phenotype. Biochemical results confirm this finding with double knockout mice showing similar metabolite accumulations as Gcdh-/- mice with high GA in brain and liver. This suggests that DHTKD1 inhibition alone is not sufficient to treat GA-I, but instead a more complex strategy is needed. Our data highlights the many unresolved questions within the l-lysine degradation pathway and provides evidence for a so far unknown mechanism leading to glutaryl-CoA.

Experiences during newborn screening for glutaric aciduria type 1: Diagnosis, treatment, genotype, phenotype, and outcomes.

BACKGROUND: Glutaric aciduria type 1 (GA-1) is an organic acidemia with potentially severe neurological sequelae. In Taiwan, newborn screening (NBS) for GA-1 began in 2001, but large-scale reporting is lacking. This study describes Taiwan's largest newborn screening population to date. METHODS: Between 2001 and 2015, 1,490,636 newborns were screened for GA-1. Confirmatory examinations included the carnitine loading test. Confirmed patients were treated with a low lysine diet, carnitine, and high-energy intake during illness. Clinical, laboratory, and neuroimaging data were analyzed. RESULTS: Fourteen newborns were diagnosed with GA-1 (incidence: 1/106,474). C5DC concentration was clearly increased after carnitine loading in the affected newborns, but not in false-positive newborns (p = 0.004), indicating that this test is useful as an adjuvant diagnostic method. Eleven patients followed in our hospital were enrolled, namely nine NBS patients and two patients diagnosed clinically. IVS10-2A>C was the most common mutation. Two novel mutations (T36fs and N291K) were identified. Pendular nystagmus was found in two pediatric GA-1 patients. The corresponding pathology was optic atrophy in one patient, but remained undetermined in the other patient. The frequency of encephalopathic crisis decreased substantially following NBS. Among patients diagnosed by NBS, cognitive functioning was better among patients with good compliance than patients with poor compliance (p = 0.03). Abnormalities were detected by brain MRI including diffusion-weighted imaging and apparent diffusion coefficient maps; these affected various brain regions at different stages of the disease. Basal ganglion injuries occurred after an encephalopathic crisis. White matter disease was prevalent among older patients, either with or without an encephalopathic crisis. CONCLUSION: Early diagnosis by newborn screening followed by full compliance with treatment guidelines is important to a good outcome.