Mutation analysis and prenatal diagnosis in a Chinese family with succinic semialdehyde dehydrogenase and a systematic review of the literature of reported ALDH5A1 mutations

Clinical features and ALDH5A1 gene findings in 13 Chinese cases with succinic semialdehyde dehydrogenase deficiency

BACKGROUND AND AIMS

To investigate the clinical features, ALDH5A1 gene variations, treatment, and prognosis of patients with succinic semialdehyde dehydrogenase (SSADH) deficiency.

MATERIALS AND METHODS

This retrospective study evaluated the findings in 13 Chinese patients with SSADH deficiency admitted to the Pediatric Department of Peking University First Hospital from September 2013 to September 2023.

RESULTS

Thirteen patients (seven male and six female patients; two sibling sisters) had the symptoms aged from 1 month to 1 year. Their urine 4-hydroxybutyrate acid levels were elevated and were accompanied by mildly increased serum lactate levels. Brain magnetic resonance imaging (MRI) showed symmetric abnormal signals in both sides of the globus pallidus and other areas. All 13 patients had psychomotor retardation, with seven showing epileptic seizures. Among the 18 variants of the ALDH5A1 gene identified in these 13 patients, six were previously reported, while 12 were novel variants. Among the 12 novel variants, three (c.85_116del, c.206_222dup, c.762C > G) were pathogenic variants; five (c.427delA, c.515G > A, c.637C > T, c.755G > T, c.1274T > C) were likely pathogenic; and the remaining four (c.454G > C, c.479C > T, c.1480G > A, c.1501G > C) were variants of uncertain significance. The patients received drugs such as L-carnitine, vigabatrin, and taurine, along with symptomatic treatment. Their urine 4-hydroxybutyric acid levels showed variable degrees of reduction.

CONCLUSIONS

A cohort of 13 cases with early-onset SSADH deficiency was analyzed. Onset of symptoms occurred from 1 month to 1 year of age. Twelve novel variants of the ALDH5A1 gene were identified.

Understanding the Molecular Mechanisms of Succinic Semialdehyde Dehydrogenase Deficiency (SSADHD): Towards the Development of SSADH-Targeted Medicine

Succinic semialdehyde dehydrogenase deficiency (SSADHD) is a rare genetic disorder caused by inefficient metabolic breakdown of the major inhibitory neurotransmitter, γ-aminobutyric acid (GABA). Pathologic brain accumulation of GABA and γ-hydroxybutyrate (GHB), a neuroactive by-product of GABA catabolism, leads to a multitude of molecular abnormalities beginning in early life, culminating in multifaceted clinical presentations including delayed psychomotor development, intellectual disability, hypotonia, and ataxia. Paradoxically, over half of patients with SSADHD also develop epilepsy and face a significant risk of sudden unexpected death in epilepsy (SUDEP). Here, we review some of the relevant molecular mechanisms through which impaired synaptic inhibition, astrocytic malfunctions and myelin defects might contribute to the complex SSADHD phenotype. We also discuss the gaps in knowledge that need to be addressed for the implementation of successful gene and enzyme replacement SSADHD therapies. We conclude with a description of a novel SSADHD mouse model that enables 'on-demand' SSADH restoration, allowing proof-of-concept studies to fine-tune SSADH restoration in preparation for eventual human trials.

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.

The regulatory role of microRNA-mRNA co-expression in hepatitis B virus-associated acute liver failure

INTRODUCTION AND OBJECTIVES

Acute liver failure (ALF) is a dramatic disorder requiring intensive care. MicroRNAs (miRNAs) have been identified to play important roles in ALF. This study was performed to identify miRNA-mRNA co-expression network after ALF to investigate the molecule mechanism underlying the pathogenesis of ALF.

MATERIALS AND METHODS

The microarray dataset GSE62030 and GSE62029 were downloaded from Gene Expression Omnibus database. Overlapping differentially expressed miRNAs (DEmiRNAs) and genes (DEGs) were identified in liver tissues from patients with hepatitis B virus (HBV)-associated ALF in comparison with normal tissues from donors. Gene enrichment analysis was performed. Key pathways associated with the DEGs were identified. The miRNA-mRNA regulatory network was constructed.

RESULTS

Total 42 DEmiRNAs and 523 DEGs were identified in liver tissues from patients with HBV-associated ALF. Gene ontology and pathways enrichment analysis showed upregulated DEGs were related to immune responses, inflammation, and infection, and downregulated DEGs were associated with amino acids, secondary metabolites and xenobiotics metabolism. In miRNA-mRNA co-expression network, DEGs were regulated by at least one DEmiRNA and transcription factor. Further analysis showed DEmiRNAs, including has-miR-55-5p, has-miR-193b-5p, has-miR-200b-3p, and has-miR-3175 were associated with amino acid metabolism, drug metabolism and detoxication, and signaling pathways including mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K)/AKT, Ras, and Rap1.

CONCLUSIONS

These miRNA-mRNA pairs and changed profiles were associated with and might be responsible for the impairment of detoxification and metabolism induced by HBV-associated ALF.

A Missense Variant in ALDH5A1 Associated with Canine Succinic Semialdehyde Dehydrogenase Deficiency (SSADHD) in the Saluki Dog

Dogs provide highly valuable models of human disease due to the similarity in phenotype presentation and the ease of genetic analysis. Seven Saluki puppies were investigated for neurological abnormalities including seizures and altered behavior. Magnetic resonance imaging showed a diffuse, marked reduction in cerebral cortical thickness, and symmetrical T2 hyperintensity in specific brain regions. Cerebral cortical atrophy with vacuolation (status spongiosus) was noted on necropsy. Genome-wide association study of 7 affected and 28 normal Salukis revealed a genome-wide significantly associated region on CFA 35. Whole-genome sequencing of three confirmed cases from three different litters revealed a homozygous missense variant within the aldehyde dehydrogenase 5 family member A1 (ALDH5A1) gene (XM_014110599.2: c.866G>A; XP_013966074.2: p.(Gly288Asp). ALDH5A1 encodes a succinic semialdehyde dehydrogenase (SSADH) enzyme critical in the gamma-aminobutyric acid neurotransmitter (GABA) metabolic pathway. Metabolic screening of affected dogs showed markedly elevated gamma-hydroxybutyric acid in serum, cerebrospinal fluid (CSF) and brain, and elevated succinate semialdehyde in urine, CSF and brain. SSADH activity in the brain of affected dogs was low. Affected Saluki dogs had striking similarities to SSADH deficiency in humans although hydroxybutyric aciduria was absent in affected dogs. ALDH5A1-related SSADH deficiency in Salukis provides a unique translational large animal model for the development of novel therapeutic strategies.

Functional analysis of thirty-four suspected pathogenic missense variants in ALDH5A1 gene associated with succinic semialdehyde dehydrogenase deficiency

Deficiency of succinate semialdehyde dehydrogenase (SSADH; aldehyde dehydrogenase 5a1 (ALDH5A1), OMIM 271980, 610045), the second enzyme of GABA degradation, represents a rare autosomal-recessively inherited disorder which manifests metabolically as gamma-hydroxybutyric aciduria. The neurological phenotype includes intellectual disability, autism spectrum, epilepsy and sleep and behavior disturbances. Approximately 70 variants have been reported in the ALDH5A1 gene, half of them being missense variants. In this study, 34 missense variants, of which 22 novel, were evaluated by in silico analyses using PolyPhen2 and SIFT prediction tools. Subsequently, the effect of these variants on SSADH activity was studied by transient overexpression in HEK293 cells. These studies showed severe enzymatic activity impairment for 27 out of 34 alleles, normal activity for one allele and a broad range of residual activities (25 to 74%) for six alleles. To better evaluate the alleles that showed residual activity above 25%, we generated an SSADH-deficient HEK293-Flp-In cell line using CRISPR-Cas9, in which these alleles were stably expressed. This model proved essential in the classification as deficient for one out of the seven studied alleles. For 8 out of 34 addressed alleles, there were discrepant results among the used prediction tools, and/or in correlating the results of the prediction tools with the functional data. In case of diagnostic urgency of missense alleles, we propose the use of the transient transfection model for confirmation of their effect on the SSADH catalytic function, since this model resulted in fast and robust functional characterization for the majority of the tested variants. In selected cases, stable transfections can be considered and may prove valuable.

Metabolic Stroke: A Novel Presentation in a Child with Succinic Semialdehyde Dehydrogenase Deficiency

Succinic semialdehyde dehydrogenase (SSADH) deficiency is an autosomal recessive disorder of gamma-aminobutyric acid metabolism. Children with SSADH deficiency usually manifest with developmental delay, behavioral symptoms, language dysfunction, seizures, hypotonia, extrapyramidal symptoms, and ataxia. Diagnosis of SSADH deficiency is established by an abnormal urine organic acid pattern, including increased excretion of 4-hydroxybutyric acid and the identification of biallelic pathogenic variants in aldehyde dehydrogenase 5 family, member A 1 (ALDH5A1) gene. Here, we describe a 15-month-old girl with SSADH deficiency presenting with developmental delay, language deficits, and acute-onset right hemiparesis, following recovery from a diarrheal illness. Brain magnetic resonance imaging revealed hyperintense signal changes involving the left globus pallidus in T2-weighted images with restriction of diffusion in the diffusion-weighted images. Increased excretion of 4-hydroxybutyric acid, threo-4,5-dihydroxyhexanoic acid lactone and erythro-4,5-dihydroxyhexanoic acid lactone was detected by urine organic acid analysis and a diagnosis of SSADH deficiency was confirmed by the identification of homozygous pathogenic variant in ALDH5A1. Stroke mimic is a novel presentation in our patient with SSADH deficiency. She was initiated on treatment with vigabatrin and has shown developmental gains with the recovery of right hemiparesis. Follow-up neuroimaging shows near complete resolution of signal changes in the left globus pallidus, while there was subtle hyperintensity in the right globus pallidus. The phenotypic spectrum of SSADH deficiency is widely expanding, and this disorder should be considered in the differential diagnosis of children with metabolic stroke.

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.

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.