Natural history of succinic semialdehyde dehydrogenase deficiency through adulthood

The continuously evolving phenotype of succinic semialdehyde dehydrogenase deficiency

The objective of the study is to evaluate the evolving phenotype and genetic spectrum of patients with succinic semialdehyde dehydrogenase deficiency (SSADHD) in long-term follow-up. Longitudinal clinical and biochemical data of 22 pediatric and 9 adult individuals with SSADHD from the patient registry of the International Working Group on Neurotransmitter related Disorders (iNTD) were studied with in silico analyses, pathogenicity scores and molecular modeling of ALDH5A1 variants. Leading initial symptoms, with onset in infancy, were developmental delay and hypotonia. Year of birth and specific initial symptoms influenced the diagnostic delay. Clinical phenotype of 26 individuals (median 12 years, range 1.8-33.4 years) showed a diversifying course in follow-up: 77% behavioral problems, 76% coordination problems, 73% speech disorders, 58% epileptic seizures and 40% movement disorders. After ataxia, dystonia (19%), chorea (11%) and hypokinesia (15%) were the most frequent movement disorders. Involvement of the dentate nucleus in brain imaging was observed together with movement disorders or coordination problems. Short attention span (78.6%) and distractibility (71.4%) were the most frequently behavior traits mentioned by parents while impulsiveness, problems communicating wishes or needs and compulsive behavior were addressed as strongly interfering with family life. Treatment was mainly aimed to control epileptic seizures and psychiatric symptoms. Four new pathogenic variants were identified. In silico scoring system, protein activity and pathogenicity score revealed a high correlation. A genotype/phenotype correlation was not observed, even in siblings. This study presents the diversifying characteristics of disease phenotype during the disease course, highlighting movement disorders, widens the knowledge on the genotypic spectrum of SSADHD and emphasizes a reliable application of in silico approaches.

Consensus guidelines for the diagnosis and management of succinic semialdehyde dehydrogenase deficiency

Succinic semialdehyde dehydrogenase deficiency (SSADHD) (OMIM #271980) is a rare autosomal recessive metabolic disorder caused by pathogenic variants of ALDH5A1. Deficiency of SSADH results in accumulation of γ-aminobutyric acid (GABA) and other GABA-related metabolites. The clinical phenotype of SSADHD includes a broad spectrum of non-pathognomonic symptoms such as cognitive disabilities, communication and language deficits, movement disorders, epilepsy, sleep disturbances, attention problems, anxiety, and obsessive-compulsive traits. Current treatment options for SSADHD remain supportive, but there are ongoing attempts to develop targeted genetic therapies. This study aimed to create consensus guidelines for the diagnosis and management of SSADHD. Thirty relevant statements were initially addressed by a systematic literature review, resulting in different evidence levels of strength according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria. The highest level of evidence (level A), based on randomized controlled trials, was unavailable for any of the statements. Based on cohort studies, Level B evidence was available for 12 (40%) of the statements. Thereupon, through a process following the Delphi Method and directed by the Appraisal of Guidelines for Research and Evaluation (AGREE II) criteria, expert opinion was sought, and members of an SSADHD Consensus Group evaluated all the statements. The group consisted of neurologists, epileptologists, neuropsychologists, neurophysiologists, metabolic disease specialists, clinical and biochemical geneticists, and laboratory scientists affiliated with 19 institutions from 11 countries who have clinical experience with SSADHD patients and have studied the disorder. Representatives from parent groups were also included in the Consensus Group. An analysis of the survey's results yielded 25 (83%) strong and 5 (17%) weak agreement strengths. These first-of-their-kind consensus guidelines intend to consolidate and unify the optimal care that can be provided to individuals with SSADHD.

Revolutionizing Blood Collection: Innovations, Applications, and the Potential of Microsampling Technologies for Monitoring Metabolites and Lipids

Blood serves as the primary global biological matrix for health surveillance, disease diagnosis, and response to drug treatment, holding significant promise for personalized medicine. The diverse array of lipids and metabolites in the blood provides a snapshot of both physiological and pathological processes, with many routinely monitored during conventional wellness checks. The conventional method involves intravenous blood collection, extracting a few milliliters via venipuncture, a technique limited to clinical settings due to its dependence on trained personnel. Microsampling methods have evolved to be less invasive (collecting ≤150 µL of capillary blood), user-friendly (enabling self-collection), and suitable for remote collection in longitudinal studies. Dried blood spot (DBS), a pioneering microsampling technique, dominates clinical and research domains. Recent advancements in device technology address critical limitations of classical DBS, specifically variations in hematocrit and volume. This review presents a comprehensive overview of state-of-the-art microsampling devices, emphasizing their applications and potential for monitoring metabolites and lipids in blood. The scope extends to diverse areas, encompassing population studies, nutritional investigations, drug discovery, sports medicine, and multi-omics research.

Reduced evoked cortical beta and gamma activity and neuronal synchronization in succinic semialdehyde dehydrogenase deficiency, a disorder of γ-aminobutyric acid metabolism

Succinic semialdehyde dehydrogenase deficiency is a rare autosomal recessively inherited metabolic disorder of γ-aminobutyric acid catabolism manifested by intellectual disability, expressive aphasia, movement disorders, psychiatric ailments and epilepsy. Subjects with succinic semialdehyde dehydrogenase deficiency are characterized by elevated γ-aminobutyric acid and related metabolites, such as γ-guanidinobutyric acid, and an age-dependent downregulation of cerebral γ-aminobutyric acid receptors. These findings indicate impaired γ-aminobutyric acid and γ-aminobutyric acid sub-type A (GABAA) receptor signalling as major factors underlying the pathophysiology of this neurometabolic disorder. We studied the cortical oscillation patterns and their relationship with γ-aminobutyric acid metabolism in 18 children affected by this condition and 10 healthy controls. Using high-density EEG, we recorded somatosensory cortical responses and resting-state activity. Using electrical source imaging, we estimated the relative power changes (compared with baseline) in both stimulus-evoked and stimulus-induced responses for physiologically relevant frequency bands and resting-state power. Stimulus-evoked oscillations are phase locked to the stimulus, whereas induced oscillations are not. Power changes for both evoked and induced responses as well as resting-state power were correlated with plasma γ-aminobutyric acid and γ-guanidinobutyric acid concentrations and with cortical γ-aminobutyric acid measured by proton magnetic resonance spectroscopy. Plasma γ-aminobutyric acid, γ-guanidinobutyric acid and cortical γ-aminobutyric acid were higher in patients than in controls (P < 0.001 for both). Beta and gamma relative power were suppressed for evoked responses in patients versus controls (P < 0.01). No group differences were observed for induced activity (P > 0.05). The mean gamma frequency of evoked responses was lower in patients versus controls (P = 0.002). Resting-state activity was suppressed in patients for theta (P = 0.011) and gamma (P < 0.001) bands. Evoked power changes were inversely correlated with plasma γ-aminobutyric acid and with γ-guanidinobutyric acid for beta (P < 0.001) and gamma (P < 0.001) bands. Similar relationships were observed between the evoked power changes and cortical γ-aminobutyric acid for all tested areas in the beta band (P < 0.001) and for the posterior cingulate gyrus in the gamma band (P < 0.001). We also observed a negative correlation between resting-state activity and plasma γ-aminobutyric acid and γ-guanidinobutyric acid for theta (P < 0.001; P = 0.003), alpha (P = 0.003; P = 0.02) and gamma (P = 0.02; P = 0.01) bands. Our findings indicate that increased γ-aminobutyric acid concentration is associated with reduced sensory-evoked beta and gamma activity and impaired neuronal synchronization in patients with succinic semialdehyde dehydrogenase deficiency. This further elucidates the pathophysiology of this neurometabolic disorder and serves as a potential biomarker for therapeutic trials.

Sensorineural Hearing Loss in a Child with Succinic Semialdehyde Dehydrogenase Deficiency

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal-recessive disorder of gamma-aminobutyric acid (GABA) metabolism, resulting in accumulation of GABA and gamma-hydroxybutyric acid (GHB) in physiological fluids. Approximately 450 patients have been diagnosed worldwide with this inherited neurotransmitter disorder. We report on a five-year-old male patient, homozygous for the pathogenic variant (NM_170740:c.1265G>A) in ALDH5A1 presenting with an unexpected association of typical SSADH deficiency manifestations with bilateral sensorineural hearing loss (SNHL). Brainstem evoked response audiometry (BERA) testing showed mid-frequency sensorineural hearing damage that suggested a hereditary component to SNHL. Whole exome sequencing (WES) failed to discern other genetic causes of deafness. Several variants of uncertain significance (VUS) detected in genes known for their role in hearing physiology could not be verified as the cause for the SNHL. It is known that central auditory processing depends on a delicate balance between excitatory and inhibitory neurotransmission, and GABA is known to play a significant role in this process. Additionally, excessive concentrations of accumulated GABA and GBH are known to cause a down-regulation of GABA receptors, which could have an adverse influence on hearing function. However, these mechanisms are very speculative in context of SNHL in a patient with inherited disorder of GABA metabolism. Injury of the globi pallidi, one of hallmarks of SSADH deficiency, could also be a contributory factor to SNHL, as was suspected in some other inborn errors in metabolism. We hope that this case will contribute to the understanding of phenotypic complexity of SSADH deficiency.

Transcranial Magnetic Stimulation in Succinic Semialdehyde Dehydrogenase Deficiency: A Measure of Maturational Trajectory of Cortical Excitability

BACKGROUND

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a disorder of GABA degradation with use-dependent downregulation of postsynaptic GABA_A/B receptors. We aim to measure the resulting cortical excitation: inhibition ratio using transcranial magnetic stimulation.

METHODS

In this single-center observational study, 18 subjects with SSADHD and 8 healthy controls underwent transcranial magnetic stimulation. Resting motor threshold, cortical silent period, and long-interval intracortical inhibition were measured in both groups. Resting motor threshold in focal epilepsy patients from an institutional transcranial magnetic stimulation database were also included.

RESULTS

SSADHD subjects had higher resting motor threshold than healthy controls but lower relative to focal epilepsy patients. Resting motor threshold decreased with age in all groups. Cortical silent period was longer in SSADHD subjects than in healthy controls. No difference was detected in long-interval intracortical inhibition between the 2 groups.

CONCLUSION

Findings suggest abnormal corticospinal tract physiology in SSADHD, but with preserved developmental trajectory for corticospinal tract maturation. Defining features of these transcranial magnetic stimulation metrics in SSADHD will be better elucidated through this ongoing longitudinal study.

Assessment of intellectual impairment, health-related quality of life, and behavioral phenotype in patients with neurotransmitter related disorders: Data from the iNTD registry

Inherited disorders of neurotransmitter metabolism are a group of rare diseases, which are caused by impaired synthesis, transport, or degradation of neurotransmitters or cofactors and result in various degrees of delayed or impaired psychomotor development. To assess the effect of neurotransmitter deficiencies on intelligence, quality of life, and behavior, the data of 148 patients in the registry of the International Working Group on Neurotransmitter Related Disorders (iNTD) was evaluated using results from standardized age-adjusted tests and questionnaires. Patients with a primary disorder of monoamine metabolism had lower IQ scores (mean IQ 58, range 40-100) within the range of cognitive impairment (<70) compared to patients with a BH₄ deficiency (mean IQ 84, range 40-129). Short attention span and distractibility were most frequently mentioned by parents, while patients reported most frequently anxiety and distractibility when asked for behavioral traits. In individuals with succinic semialdehyde dehydrogenase deficiency, self-stimulatory behaviors were commonly reported by parents, whereas in patients with dopamine transporter deficiency, DNAJC12 deficiency, and monoamine oxidase A deficiency, self-injurious or mutilating behaviors have commonly been observed. Phobic fears were increased in patients with 6-pyruvoyltetrahydropterin synthase deficiency, while individuals with sepiapterin reductase deficiency frequently experienced communication and sleep difficulties. Patients with BH₄ deficiencies achieved significantly higher quality of life as compared to other groups. This analysis of the iNTD registry data highlights: (a) difference in IQ and subdomains of quality of life between BH₄ deficiencies and primary neurotransmitter-related disorders and (b) previously underreported behavioral traits.

Enantiomers of 2-methylglutamate and 2-methylglutamine selectively impact mouse brain metabolism and behavior

Imbalance of excitatory and inhibitory neurotransmission is implicated in a wide range of psychiatric and neurologic disorders. Here we tested the hypothesis that insertion of a methyl group on the stereogenic alpha carbon of l-Glu or l-Gln would impact the γ-aminobutyric acid (GABA) shunt and the glutamate-glutamine cycle. (S)-2-methylglutamate, or (S)-2MeGlu, was efficiently transported into brain and synaptosomes where it was released by membrane depolarization in a manner equivalent to endogenous l-Glu. (R)-2MeGlu was transported less efficiently into brain and synaptosomes but was not released by membrane depolarization. Each enantiomer of 2MeGlu had limited activity across a panel of over 30 glutamate and GABA receptors. While neither enantiomer of 2MeGlu was metabolized along the GABA shunt, (S)-2MeGlu was selectively converted to (S)-2-methylglutamine, or (S)-2MeGln, which was subsequently slowly hydrolyzed back to (S)-2MeGlu in brain. rac-2MeGln was also transported into brain, with similar efficiency as (S)-2MeGlu. A battery of behavioral tests in young adult wild type mice showed safety with up to single 900 mg/kg dose of (R)-2MeGlu, (S)-2MeGlu, or rac-2MeGln, suppressed locomotor activity with single ≥ 100 mg/kg dose of (R)-2MeGlu or (S)-2MeGlu. No effect on anxiety or hippocampus-dependent learning was evident. Enantiomers of 2MeGlu and 2MeGln show promise as potential pharmacologic agents and imaging probes for cells that produce or transport l-Gln.

123I-FP-CIT Brain SPECT Findings in Succinic Semialdehyde Dehydrogenase (SSADH) Deficiency

BACKGROUND

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessive disorder. Neuroimaging findings are commonly considered rather non-specific. To date, no neuroreceptorial brain imaging with ¹²³I-FP-CIT(DaTScan) is known in subjects with SSADH deficiency.

METHODS

A 30-year-old man gained our attention to rule out any potential nigrostriatal dopaminergic presynaptic pathway alterations in a clinical context of a γ-hydroxybutyric aciduria. He showed impossibility to the autonomous gait, head and trunk retropulsion, lower limbs strength deficit, verbal and upper limbs motor stereotypies and irregular eye tracking.

RESULTS

His brain MRI depicted basal ganglia signal abnormalities. Brain SPECT with DaTSCan images showed a global significant reduction of radiotracer uptake.

CONCLUSIONS

The findings obtained by means of the ¹²³I-DaTScan brain SPECT may give rise to new concerns on pathophysiological aspects of the SSADH deficiency disorder that has never been investigated before, such as the nigrostriatal dopaminergic system's functionality, encouraging further investigation.

Enzyme Replacement Therapy for Succinic Semialdehyde Dehydrogenase Deficiency: Relevance in γ-Aminobutyric Acid Plasticity

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare inborn metabolic disorder caused by the functional impairment of SSADH (encoded by the ALDH5A1 gene), an enzyme essential for metabolism of the inhibitory neurotransmitter γ-aminobutyric acid (GABA). In SSADHD, pathologic accumulation of GABA and its metabolite γ-hydroxybutyrate (GHB) results in broad spectrum encephalopathy including developmental delay, ataxia, seizures, and a heightened risk of sudden unexpected death in epilepsy (SUDEP). Proof-of-concept systemic SSADH restoration via enzyme replacement therapy increased survival of SSADH knockout mice, suggesting that SSADH restoration might be a viable intervention for SSADHD. However, before testing enzyme replacement therapy or gene therapy in patients, we must consider its safety and feasibility in the context of early brain development and unique SSADHD pathophysiology. Specifically, a profound use-dependent downregulation of GABA_A receptors in SSADHD indicates a risk that any sudden SSADH restoration might diminish GABAergic tone and provoke seizures. In addition, the tight developmental regulation of GABA circuit plasticity might limit the age window when SSADH restoration is accomplished safely. Moreover, given SSADH expressions are cell type-specific, targeted instead of global restoration might be necessary. We therefore describe 3 key parameters for the clinical readiness of SSADH restoration: (1) rate, (2) timing, and (3) cell type specificity. Our work focuses on the construction of a novel SSADHD mouse model that allows "on-demand" SSADH restoration for the systematic investigation of these key parameters. We aim to understand the impacts of specific SSADH restoration protocols on brain physiology, accelerating bench-to-bedside development of enzyme replacement therapy or gene therapy for SSADHD patients.

Succinic Semialdehyde Dehydrogenase Deficiency: Review of the Natural History Study

OBJECTIVE

The SSADHD Natural History Study was initiated in 2019 to define the natural course and identify biomarkers correlating with severity.

METHODS

The study is conducted by 4 institutions: BCH (US clinical), WSU (bioanalytical core), USF (biostatistical core), and Heidelberg (iNTD), with support from the family advocacy group (SSADH Association). Recruitment goals were to study 20 patients on-site at BCH, 10 with iNTD, and 25 as a standard-of care cohort.

RESULTS

At this half-way point of this longitudinal study, 28 subjects have been recruited (57% female, mean 9 years, range 18 months-40 years). Epilepsy is present in half and increases in incidence and severity, as do psychiatric symptoms, in adolescence and adulthood. The average Full Scale IQ (FSIQ) was 53 (Verbal score of 56, Non Verbal score of 49), and half scored as having ASD. Although there was no correlation between gene variant and phenotypic severity, there were extreme cases of lowest functioning in one individual and highest in another that may have genotype-phenotype correlation. The most common EEG finding was mild background slowing with rare epileptiform activity, whereas high-density EEG and magnetoencephalography showed reduction in the gamma frequency band consistent with GABAergic dysfunction. MR spectroscopy showed elevations in the GABA/NAA ratio in all regions studied with no crossover between subjects and controls.

CONCLUSIONS

The SSADH Natural History Study is providing a unique opportunity to study the complex pathophysiology longitudinally and derive electrophysiologic, neuroimaging, and laboratory data for correlation and to serve as biomarkers for clinical trials and prognostic assessments in this ultra-rare inherited disorder of GABA metabolism.

Succinic semialdehyde dehydrogenase deficiency presenting with central hypothyroidism

Central hypothyroidism might be another clinical sign of SSADH deficiency which prompts urinary organic acid screening for GHB in central hypothyroidism patients. Studies on GABA and thyroid hormone interaction might be a concept of a new therapy.

Epilepsy in inherited neurotransmitter disorders: Spotlights on pathophysiology and clinical management

Inborn errors of neurotransmitter metabolism are ultrarare disorders affecting neurotransmitter biosynthesis, breakdown or transport or their essential cofactors. Neurotransmitter dysfunctions could also result from the impairment of neuronal receptors, intracellular signaling, vesicle release or other synaptic abnormalities. Epilepsy is the main clinical hallmark in some of these diseases (e.g. disorders of GABA metabolism, glycine encephalopathy) while it is infrequent in others (e.g. all the disorders of monoamine metabolism in exception for dihydropteridine reductase deficiency). This review analyzes the epileptogenic mechanisms, the epilepsy phenotypes and the principle for the clinical management of epilepsy in primary and secondary inherited disorders of neurotransmitter metabolism (disorders of GABA, serine and glycine metabolism, disorders of neurotransmitter receptors and secondary neurotransmitter diseases).

Succinic Semialdehyde Dehydrogenase Deficiency: In Vitro and In Silico Characterization of a Novel Pathogenic Missense Variant and Analysis of the Mutational Spectrum of ALDH5A1

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare, monogenic disorder affecting the degradation of the main inhibitory neurotransmitter γ-amino butyric acid (GABA). Pathogenic variants in the ALDH5A1 gene that cause an enzymatic dysfunction of succinic semialdehyde dehydrogenase (SSADH) lead to an accumulation of potentially toxic metabolites, including γ-hydroxybutyrate (GHB). Here, we present a patient with a severe phenotype of SSADHD caused by a novel genetic variant c.728T > C that leads to an exchange of leucine to proline at residue 243, located within the highly conserved nicotinamide adenine dinucleotide (NAD)⁺ binding domain of SSADH. Proline harbors a pyrrolidine within its side chain known for its conformational rigidity and disruption of protein secondary structures. We investigate the effect of this novel variant in vivo, in vitro, and in silico. We furthermore examine the mutational spectrum of all previously described disease-causing variants and computationally assess all biologically possible missense variants of ALDH5A1 to identify mutational hotspots.

Novel ALDH5A1 variants and genotype: Phenotype correlation in SSADH deficiency

OBJECTIVE

To determine genotype-phenotype correlation in succinic semialdehyde dehydrogenase (SSADH) deficiency.

METHODS

ALDH5A1 variants were studied with phenotype correlation in the SSADH natural history study. Assignment of gene variant pathogenicity was based on in silico testing and in vitro enzyme activity after site-directed mutagenesis and expression in HEK293 cells. Phenotypic scoring used a Clinical Severity Score (CSS) designed for the natural history study.

RESULTS

Twenty-four patients were enrolled (10 male, 14 female, median age 8.2 years). There were 24 ALDH5A1 variants, including 7 novel pathogenic variants: 2 missense, 3 splice site, and 2 frameshift. Four previously reported variants were identified in >5% of unrelated families. There was a correlation with age and presence (p = 0.003) and severity (p = 0.002) of epilepsy and with obsessive-compulsive disorder (OCD) (p = 0.016). The median IQ score was 53 (Q25-Q75, 49-61). There was no overall correlation between the gene variants and the CSS, although a novel missense variant was associated with the mildest phenotype by CSS in the only patient with a normal IQ, whereas a previously reported variant was consistently associated with the most severe phenotype.

CONCLUSIONS

Seven novel pathogenic and one previously unpublished benign ALDH5A1 variants were detected. There is an age-dependent association with worsening of epilepsy and presence of OCD in SSADH deficiency. Overall, there does not appear to be a correlation between genotype and phenotypic severity in this cohort of 24 patients. We did find a suspected correlation between a novel pathogenic missense variant and high functionality, and a previously reported pathogenic missense variant and maximal severity.

OCD symptoms in succinic semialdehyde dehydrogenase (SSADH) deficiency: a case report

BACKGROUND

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare neurometabolic disorder resulting in a heterogeneous clinical phenotype. Adolescent and adult patients with SSADH deficiency may present with OCD symptoms. There is minimal literature regarding the pathological basis of OCD symptoms and their management amongst SSADH deficiency patients.

CASE PRESENTATION

A 26-year-old woman with SSADH deficiency experienced obsessional slowness and hesitancy in her activities of daily living, with motor rituals and stereotypies of her hands and face. Neuroimaging revealed T2 hyperintensities of the globi pallidi bilaterally. Commencement of the serotonergic escitalopram moderately improved her OCD symptoms. The addition of the dopaminergic pramipexole hydrochloride yielded further improvement, following unsuccessful trial of other adjuncts: risperidone, methylphenidate and mirtazapine.

CONCLUSIONS

Pallidal pathology may explain the manifestation of OCD symptoms amongst individuals with SSADH deficiency. Serotonergic and concomitant dopaminergic therapy may be a viable treatment regimen for SSADH deficiency patients presenting with OCD symptoms.

Longitudinal metabolomics in dried bloodspots yields profiles informing newborn screening for succinic semialdehyde dehydrogenase deficiency

Analyses of 19 amino acids, 38 acylcarnitines, and 3 creatine analogues (https://clir.mayo.edu) were implemented to test the hypothesis that succinic semialdehyde dehydrogenase deficiency (SSADHD) could be identified in dried bloodspots (DBS) using currently available newborn screening methodology. The study population included 17 post-newborn SSADHD DBS (age range 0.8-38 years; median, 8.2 years; 10 M; controls, 129-353 age-matched individuals, mixed gender) and 10 newborn SSADHD DBS (including first and second screens from 3 of 7 patients). Low (informative) markers in post-newborn DBS included C2- and C4-OH carnitines, ornithine, histidine and creatine, with no gender differences. For newborn DBS, informative markers included C2-, C3-, C4- and C4-OH carnitines, creatine and ornithine. Of these, only creatine demonstrated a significant change with age, revealing an approximate 4-fold decrease. We conclude that quantitation of short-chain acylcarnitines, creatine, and ornithine provides a newborn DBS profile with potential as a first tier screening tool for early detection of SSADHD. This first tier evaluation can be readily verified using a previously described second tier liquid chromatography-tandem mass spectrometry method for γ-hydroxybutyric acid in the same DBS. More extensive evaluation of this first/second tier screening approach is needed in a larger population.

Temporal metabolomics in dried bloodspots suggests multipathway disruptions in aldh5a1-/- mice, a model of succinic semialdehyde dehydrogenase deficiency

Succinic semialdehyde dehydrogenase (SSADH) deficiency (SSADHD; OMIM 271980) is a rare disorder featuring accumulation of neuroactive 4-aminobutyric acid (GABA; γ-aminobutyric acid, derived from glutamic acid) and 4-hydroxybutyric acid (γ-hydroxybutyric acid; GHB, a short-chain fatty acid analogue of GABA). Elevated GABA is predicted to disrupt the GABA shunt linking GABA transamination to the Krebs cycle and maintaining the balance of excitatory:inhibitory neurotransmitters. Similarly, GHB (or a metabolite) is predicted to impact β-oxidation flux. We explored these possibilities employing temporal metabolomics of dried bloodspots (DBS), quantifying amino acids, acylcarnitines, and guanidino- metabolites, derived from aldh5a1^+/+, aldh5a1^+/- and aldh5a1^-/- mice (aldehyde dehydrogenase 5a1 = SSADH) at day of life (DOL) 20 and 42 days. At DOL 20, aldh5a1^-/- mice had elevated C6 dicarboxylic (adipic acid) and C14 carnitines and threonine, combined with a significantly elevated ratio of threonine/[aspartic acid + alanine], in comparison to aldh5a1^+/+ mice. Conversely, at DOL 42 aldh5a1^-/- mice manifested decreased short chain carnitines (C0-C6), valine and glutamine, in comparison to aldh5a1^+/+ mice. Guanidino species, including creatinine, creatine and guanidinoacetic acid, evolved from normal levels (DOL 20) to significantly decreased values at DOL 42 in aldh5a1^-/- as compared to aldh5a1^+/+ mice. Our results provide a novel temporal snapshot of the evolving metabolic profile of aldh5a1^-/- mice while highlighting new pathomechanisms in SSADHD.

Novel mutations in two unrelated Italian patients with SSADH deficiency

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare autosomal recessive disorder of γ-aminobutyric acid (GABA) catabolism caused by mutations in the gene coding for succinic semialdehyde dehydrogenase (ALDH5A1). The abnormal levels of GHB detected in the brain and in all physiological fluids of SSADHD patients represent a diagnostic biochemical hallmark of the disease. Here we report on the clinical and molecular characterization of two unrelated Italian patients and the identification of two novel mutations: a 22 bp DNA duplication in exon 1, c.114_135dup, p.(C46AfsX97), and a non-sense mutation in exon 10, c.1429C > T, p.(Q477X). The two patients showed very different clinical phenotypes, coherent with their age. These findings enrich the characterization of SSADHD families and contribute to the knowledge on the progression of the disease.

Gamma-Hydroxybutyrate content in dried bloodspots facilitates newborn detection of succinic semialdehyde dehydrogenase deficiency

Increased gamma-hydroxybutyric acid in urine and blood are metabolic hallmarks of succinic semialdehyde dehydrogenase deficiency, a defect of 4-aminobutyric acid metabolism. Here, we examined the hypothesis that succinic semialdehyde dehydrogenase deficiency could be identified via measurement of gamma-hydroxybutyric acid in newborn and post-newborn dried bloodspots. Quantitation of gamma-hydroxybutyric acid using liquid chromatography-tandem mass spectrometry in twelve archival newborn patient dried bloodspots was 360 ± 57 μM (mean, standard error; range 111-767), all values exceeding the previously established cutoff for newborn detection of 78 μΜ established from 2831 dried bloodspots derived from newborns, neonates and children. Gamma-hydroxybutyric acid in post-newborn dried bloodspots (n = 19; ages 0.8-38 years) was 191 ± 65 μM (mean, standard error; range 20-1218), exceeding the aforementioned GHB cutoff for patients approximately 10 years of age or younger. Further, gamma-hydroxybutyric acid in post-newborn dried bloodspots displayed a significant (p < .0001) inverse correlation with age. This preliminary study suggests that succinic semialdehyde dehydrogenase deficiency may be identified in newborn and post-newborn dried bloodspots via quantitation of gamma-hydroxybutyric acid, while forming the platform for more extensive studies in affected and unaffected dried bloodspots.

Clinical diagnosis and mutation analysis of four Chinese families with succinic semialdehyde dehydrogenase deficiency

Background

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal recessively-inherited defect of γ-aminobutyric acid (GABA) metabolism. The absence of SSADH, which is encoded by aldehyde dehydrogenase family 5 member A1 (ALDH5A1) gene, leads to the accumulation of GABA and γ-hydroxybutyric acid (GHB). Few cases with SSADH deficiency were reported in China.

Case presentation

In this study, four Chinese patients were diagnosed with SSADH deficiency in Tianjin Children’s Hospital. We conducted a multidimensional analysis with magnetic resonance imaging (MRI) of the head, semi quantitative detection of urine organic acid using gas chromatography-mass spectrometry, and analysis of ALDH5A1 gene mutations.

Two of the patients were admitted to the hospital due to convulsions, and all patients were associated with developmental delay. Cerebral MRI showed symmetrical hyperintense signal of bilateral globus pallidus and basal ganglia in patient 1; hyperintensity of bilateral frontal-parietal lobe, widened ventricle and sulci in patient 2; and widened ventricle and sulci in patient 4. Electroencephalogram (EEG) revealed the background activity of epilepsy in patient 1 and the disappearance of sleep spindle in patient 2. Urine organic acid analysis revealed elevated GHB in all the patients. Mutational analysis, which was performed by sequencing the 10 exons and flanking the intronic regions of ALDH5A1 gene for all the patients, revealed mutations at five sites. Two cases had homozygous mutations with c.1529C > T and c.800 T > G respectively, whereas the remaining two had different compound heterozygous mutations including c.527G > A/c.691G > A and c.1344-2delA/c.1529C > T. Although these four mutations have been described previously, the homozygous mutation of c.800 T > G in ALDH5A1 gene is a novel discovery.

Conclusion

SSADH deficiency is diagnosed based on the elevated GHB and 4, 5DHHA by urinary organic acid analysis. We describe a novel mutation p.V267G (c.800 T > G) located in the NAD binding domain, which is possibly crucial for this disease’s severity. Our study expands the mutation spectrum of ALDH5A1 and highlights the importance of molecular genetic evaluation in patients with SSADH deficiency.

Rett syndrome (MECP2) and succinic semialdehyde dehydrogenase (ALDH5A1) deficiency in a developmentally delayed female

BACKGROUND

We present a patient with Rett syndrome (RTT; MECP2) and autosomal-recessive succinic semialdehyde dehydrogenase deficiency (SSADHD; ALDH5A1 (aldehyde dehydrogenase 5a1 = SSADH), in whom the current phenotype exhibits features of SSADHD (hypotonia, global developmental delay) and RTT (hand stereotypies, gait anomalies).

METHODS

γ-Hydroxybutyric acid (GHB) was quantified by UPLC-tandem mass spectrometry, while mutation analysis followed standard methodology of whole-exome sequencing.

RESULTS

The biochemical hallmark of SSADHD, GHB was increased in the proband's dried bloodspot (DBS; 673 µM; previous SSADHD DBSs (n = 7), range 124-4851 µM); control range (n = 2,831), 0-78 µM. The proband was compound heterozygous for pathogenic ALDH5A1 mutations (p.(Asn418IlefsTer39); maternal; p.(Gly409Asp); paternal) and a de novo RTT nonsense mutation in MECP2 (p.Arg255*).

CONCLUSION

The major inhibitory neurotransmitter, γ-aminobutyric acid (GABA), is increased in SSADHD but normal in RTT, although there are likely regional changes in GABA receptor distribution. GABAergic anomalies occur in both disorders, each featuring an autism spectrum phenotype. What effect the SSADHD biochemical anomalies (elevated GABA, GHB) might play in the neurodevelopmental/epileptic phenotype of our patient is currently unknown.

Age-related phenotype and biomarker changes in SSADH deficiency

Objective

Succinic Semialdehyde Dehydrogenase (SSADH) deficiency is a disorder of elevated gamma‐amino butyric acid (GABA) and gamma hydroxybutyric acid (GHB) and a complex neuropsychiatric profile. Adult reports suggest worsening epilepsy and high SUDEP risk.

Methods

Subjects with confirmed SSADH deficiency were recruited into a longitudinal study. Plasma thyroid hormone and total GABA/GHB were quantified by standard clinical chemistry methodologies and mass spectrometry, respectively.

Results

A total of 133 subjects with SSADH deficiency are enrolled in the registry; 49 participated in the longitudinal study. The age range of the population is 8 weeks to 63 years (median 7.75 year; 44% male). There is a significant difference in proportions among the age groups in subjects affected with hypotonia, compulsive behavior, sleep disturbances, and seizures. Epilepsy is present in 50% of the total population, and more prevalent in subjects 12 years and older (P = 0.001). The median age of onset for absence seizures was 2 years, and 12 years for generalized tonic‐clonic seizures (P < 0.01). The SUDEP rate in adults was 12% (4/33). There was a significant age‐dependent negative correlation between GABA and T₃ levels.

Interpretation

There is an age‐dependent association with worsening of epilepsy, behavioral disturbances including obsessive‐compulsive behavior, and sleep disturbances with age in SSADH deficiency. There is a high risk of SUDEP. We have observed more absence seizures in younger patients, compared to tonic‐clonic in the older cohort, which correlates with age‐related changes in GABA and GHB concentration and thyroid function, as well as the natural history of seizures in the murine model.

Impact on GABA systems in monogenetic developmental CNS disorders: Clues to symptomatic treatment

Animal studies of several single-gene disorders demonstrate that reversing the molecular signaling deficits can result in substantial symptomatic improvements in function. Focusing on the ratio of excitation to inhibition as a potential pathophysiological hallmark, seven single-gene developmental CNS disorders are reviewed which are characterized by a striking dysregulation of neuronal inhibition. Deficits in inhibition and excessive inhibition are found. The examples of developmental disorders encompass Neurofibromatosis type 1, Fragile X syndrome, Rett syndrome, Dravet syndrome including autism-like behavior, NONO-mutation-induced intellectual disability, Succinic semialdehyde dehydrogenase deficiency and Congenital nystagmus due to FRMD7 mutations. The phenotype/genotype correlations observed in animal models point to potential treatment options and will continue to inspire clinical research. Three drugs are presently in clinical trials: acamprosate and ganoxolon for Fragile X syndrome and SGS-742 for SSADH deficiency. This article is part of the "Special Issue Dedicated to Norman G. Bowery".

Outcome of childhood-onset epilepsy from adolescence to adulthood: Transition issues

This is the second of three papers that summarize the second symposium on Transition in Epilepsies held in Paris in June 2016. This paper addresses the outcome for some particularly challenging childhood-onset epileptic disorders with the goal of recommending the best approach to transition. We have grouped these disorders in five categories with a few examples for each. The first group includes disorders presenting in childhood that may have late- or adult-onset epilepsy (metabolic and mitochondrial disorders). The second group includes disorders with changing problems in adulthood (tuberous sclerosis complex, Rett syndrome, Dravet syndrome, and autism). A third group includes epilepsies that change with age (Childhood Absence Epilepsy, Juvenile Myoclonic Epilepsy, West Syndrome, and Lennox-Gastaut syndrome). A fourth group consists of epilepsies that vary in symptoms and severity depending on the age of onset (autoimmune encephalitis, Rasmussen's syndrome). A fifth group has epilepsy from structural causes that are less likely to evolve in adulthood. Finally we have included a discussion about the risk of later adulthood cerebrovascular disease and dementia following childhood-onset epilepsy. A detailed knowledge of each of these disorders should assist the process of transition to be certain that attention is paid to the most important age-related symptoms and concerns.

In vitro toxicological evaluation of NCS-382, a high-affinity antagonist of γ-hydroxybutyrate (GHB) binding

γ-Hydroxybutyric acid (GHB), a minor metabolite of the inhibitory neurotransmitter GABA, can accumulate to significant concentrations in the heritable disorder of GABA degradation, succinic semialdehyde dehydrogenase (SSADH) deficiency (SSADHD). Moreover, GHB may be employed in therapeutic settings (treatment of narcolepsy), as well as instances of illicit activity, including acquaintance sexual assault and the induction of euphoria. High-affinity binding sites for GHB in the brain have been identified, although the absolute identity of these receptors remains unclear. Pharmacological antagonism of GHB binding may have multiple instances of therapeutic relevance. The high affinity GHB receptor antagonist, NCS-382 (6,7,8,9-tetrahydro-5-hydroxy-5H-benzo-cyclohept-6-ylideneacetic acid) has not been piloted in humans. To address the potential clinical utility of NCS-382, we have piloted initial studies of its toxicology in HepG2 and primary hepatocyte cells. At high dose (0.5mM), NCS-382 showed no capacity for inhibition of microsomal CYPs (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6 and 3A4) and minimal potential for activation of xenobiotic nuclear receptors. Additional cellular integrity and functional assays (viability, oxidative stress, apoptosis, ATP production) revealed little evidence for cytotoxicity, and a low degree of dysregulation of >370 genes actively engaged in the mediation of cellular toxicity. In vitro testing indicates a low probability of cellular toxicity associated with NCS-382.

Therapeutic relevance of mTOR inhibition in murine succinate semialdehyde dehydrogenase deficiency (SSADHD), a disorder of GABA metabolism

Aldehyde dehydrogenase 5a1-deficient (aldh5a1-/-) mice, the murine orthologue of human succinic semialdehyde dehydrogenase deficiency (SSADHD), manifest increased GABA (4-aminobutyric acid) that disrupts autophagy, increases mitochondria number, and induces oxidative stress, all mitigated with the mTOR (mechanistic target of rapamycin) inhibitor rapamycin [1]. Because GABA regulates mTOR, we tested the hypothesis that aldh5a1-/- mice would show altered levels of mRNA for genes associated with mTOR signaling and oxidative stress that could be mitigated by inhibiting mTOR. We observed that multiple metabolites associated with GABA metabolism (γ-hydroxybutyrate, succinic semialdehyde, D-2-hydroxyglutarate, 4,5-dihydrohexanoate) and oxidative stress were significantly increased in multiple tissues derived from aldh5a1-/- mice. These metabolic perturbations were associated with decreased levels of reduced glutathione (GSH) in brain and liver of aldh5a1-/- mice, as well as increased levels of adducts of the lipid peroxidation by-product, 4-hydroxy-2-nonenal (4-HNE). Decreased liver mRNA levels for multiple genes associated with mTOR signaling and oxidative stress parameters were detected in aldh5a1-/- mice, and several were significantly improved with the administration of mTOR inhibitors (Torin 1/Torin 2). Western blot analysis of selected proteins corresponding to oxidative stress transcripts (glutathione transferase, superoxide dismutase, peroxiredoxin 1) confirmed gene expression findings. Our data provide additional preclinical evidence for the potential therapeutic efficacy of mTOR inhibitors in SSADHD.

Incidence and Geographic Distribution of Succinic Semialdehyde Dehydrogenase (SSADH) Deficiency

The incidence of succinic semialdehyde dehydrogenase (SSADH) deficiency, an autosomal recessive inherited disorder of GABA degradation, is unknown. Upon a recent diagnosis of a new family of affected fraternal twins from the Punjabi ethnic group of India, case ascertainment from the literature and our database was done to determine the number of confirmed cases along with their geographic distribution. The probands presented with global developmental delay, infantile onset epilepsy, and a persistent neurodevelopmental disorder upon diagnosis at 10 years of age with intellectual disability, expressive aphasia, and behavioral problems most prominent for hyperactivity. Gamma-hydroxybutyric aciduria and homozygous ALDH5A1 c.608C>T; p.Pro203Leu mutations were confirmed. Identification of all available individual cases with clinical details available including geographic or ethnic origin revealed 182 patients from 40 countries, with the largest number of patients reported from the USA (24%), Turkey (10%), China (7%), Saudi Arabia (6%), and Germany (5%). This study provides an accounting of all published cases of confirmed SSADH deficiency and provides data useful in planning further studies of this rare inborn error of metabolism.

mTOR inhibitors rescue premature lethality and attenuate dysregulation of GABAergic/glutamatergic transcription in murine succinate semialdehyde dehydrogenase deficiency (SSADHD), a disorder of GABA metabolism

Recent studies have identified a role for supraphysiological gamma-aminobutyric acid (GABA) in the regulation of mechanistic target of rapamycin (mTOR), a protein kinase with pleiotropic roles in cellular development and homeostasis, including integration of growth factors and nutrient sensing and synaptic input in neurons (Lakhani et al. 2014; Vogel et al. 2015). Aldehyde dehydrogenase 5a1-deficient (aldh5a1 ^-/- ) mice, the murine orthologue of human succinic semialdehyde dehydrogenase deficiency (SSADHD), manifest increased GABA that disrupts mitophagy and increases mitochondria number with enhanced oxidant stress. Treatment with the mTOR inhibitor, rapamycin, significantly attenuates these GABA-related anomalies. We extend those studies through characterization of additional rapamycin analog (rapalog) agents including temsirolimus, dual mTOR inhibitors [Torin 1 and 2 (Tor 1/ Tor 2), Ku-0063794, and XL-765], as well as mTOR-independent autophagy inducers [trehalose, tat-Beclin 1, tacrolimus (FK-506), and NF-449) in aldh5a1 ^-/- mice. Rapamycin, Tor 1, and Tor 2 rescued these mice from premature lethality associated with status epilepticus. XL-765 extended lifespan significantly and induced weight gain in aldh5a1 ^-/- mice; untreated aldh5a1 ^-/- mice failed to increase body mass. Expression profiling of animals rescued with Tor 1/Tor 2 and XL-765 revealed multiple instances of pharmacological compensation and/or correction of GABAergic and glutamatergic receptors, GABA/glutamate transporters, and GABA/glutamate-associated proteins, with Tor 2 and XL-765 showing optimal outcomes. Our studies lay the groundwork for further evaluation of mTOR inhibitors in aldh5a1 ^-/- mice, with therapeutic ramifications for heritable disorders of GABA and glutamate neurotransmission.

Correlation of blood biomarkers with age informs pathomechanisms in succinic semialdehyde dehydrogenase deficiency (SSADHD), a disorder of GABA metabolism

We hypothesized that blood levels of γ-aminobutyric acid (GABA) and γ-hydroxybutyric acid (GHB), biomarkers of succinic semialdehyde dehydrogenase deficiency (SSADHD), would correlate with age. GABA and GHB were quantified in plasma and red blood cells (RBCs) from 18 patients (age range 5-41 years; median 8). Both metabolites negatively correlated with age (P < 0.05). Plasma and RBC GHB declined with age, reaching a nadir and approximate steady state by 10 years. Declining plasma GABA achieved this approximate steady state at 30-40 years of age. These biomarker relationships may reflect further GABA- and GHB-ergic neurotransmission imbalances that correlate with the onset of adolescent/adulthood neuropsychiatric morbidity and epilepsy in SSADHD.

Targeted screening of succinic semialdehyde dehydrogenase deficiency (SSADHD) employing an enzymatic assay for γ-hydroxybutyric acid (GHB) in biofluids

HYPOTHESIS

An enzymatic assay for quantification of γ-hydroxybutyric acid (GHB) in biofluids can be employed for targeted screening of succinic semialdehyde dehydrogenase deficiency (SSADHD) in selected populations.

RATIONALE

We used a two-tiered study approach, in which the first study (proof of concept) examined 7 urine samples derived from patients with SSADHD and 5 controls, and the second study (feasibility study) examined a broader sample population of patients and controls, including plasma.

OBJECTIVE

Split samples of urine and plasma (anonymized) were evaluated by enzymatic assay, gas chromatography alone (proof of concept) and gas chromatography-mass spectrometry, and the results compared.

METHOD

Multiple detection methods have been developed to detect GHB. We evaluated an enzymatic assay which employs recombinant GHB dehydrogenase coupled to NADH production, the latter quantified on a Cobas Integra 400 Plus. Results: In our proof of concept study, we analyzed 12 urine samples (5 controls, 7 SSADHD), and in the feasibility study we evaluated 33 urine samples (23 controls, 10 SSADHD) and 31 plasma samples (14 controls, 17 SSADHD). The enzymatic assay carried out on a routine clinical chemistry analyzer was robust, revealing excellent agreement with instrumental methods in urine (GC-FID: r = 0.997, p ≤ 0.001; GC-MS: r = 0.99, p ≤ 0.001); however, the assay slightly over-estimated GHB levels in plasma, especially those in which GHB levels were low. Conversely, correlations for the enzymatic assay with comparator methods for higher plasma GHB levels were excellent (GC-MS; r = 0.993, p ≤ 0.001).

CONCLUSION

We have evaluated the capacity of this enzymatic assay to identify patients with SSADHD via quantitation of GHB. The data suggests that the enzymatic assay may be a suitable screening method to detect SSADHD in selected populations using urine. In addition, the assay can be used in basic research the elucidate the mechanism of the underlying disease or monitor GHB- levels for the evaluation of drug candidates.

SYNOPSIS

An enzymatic assay for GHB in biofluids was evaluated as a screening method for SSADHD and found to be reliable in urine, but in need of refinement for application to plasma.

Succinic semialdehyde dehydrogenase deficiency (SSADHD): Pathophysiological complexity and multifactorial trait associations in a rare monogenic disorder of GABA metabolism

Discovered some 35 years ago, succinic semialdehyde dehydrogenase deficiency (SSADHD) represents a rare, autosomal recessively-inherited defect in the second step of the GABA degradative pathway. Some 200 patients have been reported, with broad phenotypic and genotypic heterogeneity. SSADHD represents an unusual neurometabolic disorder in which two neuromodulatory agents, GABA (and the GABA analogue, 4-hydroxybutyrate), accumulate to supraphysiological levels. The unexpected occurrence of epilepsy in several patients is counterintuitive in view of the hyperGABAergic state, in which sedation might be expected. However, the epileptic status of some patients is most likely represented by broader imbalances of GABAergic and glutamatergic neurotransmission. Cumulative research encompassing decades of basic and clinical study of SSADHD reveal a monogenic disease with broad pathophysiological and clinical phenotypes. Numerous metabolic perturbations unmasked in SSADHD include alterations in oxidative stress parameters, dysregulation of autophagy and mitophagy, dysregulation of both inhibitory and excitatory neurotransmitters and gene expression, and unique subsets of SNP alterations of the SSADH gene (so-called ALDH5A1, or aldehyde dehydrogenase 5A1 gene) on the 6p22 chromosomal arm. While seemingly difficult to collate and interpret, these anomalies have continued to open novel pathways for pharmacotherapeutic considerations. Here, we present an update on selected aspects of SSADHD, the ALDH5A1 gene, and future avenues for research on this rare disorder of GABA metabolism.