Succinic Semialdehyde Dehydrogenase Deficiency in a Chinese Boy: A Novel ALDH5A1 Mutation With Severe Phenotype

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.

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.

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.

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.

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".

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.

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.

Modulation of ALDH5A1 and SLC22A7 by microRNA hsa-miR-29a-3p in human liver cells

Observed variations in drug responses among patients may result from differences in heritable genetic traits or from alterations in the epigenetic regulation of drug metabolizing enzymes and transporters (DMETs). MicroRNAs (miRNAs), a group of small non-coding RNAs, provide an epigenetic mechanism for fine-tuning the expression of targeted DMET genes by regulating the efficiency of protein translation and by decreasing mRNA stability via enhanced degradation. In the current study we systematically screened 374 important genes encoding DMETs for potential response elements to hsa-miR-29a-3p, a highly abundant miRNA in human liver. RNA electrophoresis mobility shift assays displayed direct interactions between hsa-miR-29a-3p and its cognate targets within the mRNA transcripts for the ABCC6, SLC22A7 and ALDH5A1 genes. The expression of luciferase reporter genes containing the 3'-UTRs of SLC22A7 or ALDH5A1 and the expression of endogenous SLC22A7 and ALDH5A1 were each suppressed by transfection with hsa-miR-29a-3p mimics. Importantly, chemically-induced up-regulation of hsa-miR-29a-3p correlated inversely with the expression of SLC22A7 and ALDH5A1. However, our studies failed to detect suppressive effects of hsa-miR-29a-3p on ABCC6 expression, which might be explained by the notion that the interaction of hsa-miR-29a-3p and ABCC6 mRNA was unable to recruit ribonucleoproteins to form a RNA-induced silencing complex.