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 \u3b3-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 \u3b3-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

Die intrazerebrale Gentherapie des Aromatischen-L-Aminosäure-Decarboxylase-Mangels mit Eladocagene exuparvovec : Eine Stellungnahme der Gesellschaft für Neuropädiatrie (GNP), der Arbeitsgemeinschaft pädiatrischer Stoffwechselstörungen (APS), der Deutschen Gesellschaft für Neurochirurgie (DGNC) und der Deutschen Gesellschaft für Kinder- und Jugendmedizin (DGKJ)

Background The autosomal recessive defect of aromatic L‑amino acid decarboxylase (AADC) causes a severe combined deficiency of dopamine, serotonin and catecholamines. The clinical picture is characterized by truncal hypotonia, delayed or absent achievement of motor milestones, and oculogyric crises from infancy onwards. The response to conventional drug treatment is very limited, especially in severe cases. The intracerebral application of eladocagene exuparvovec, an AAV2-based gene therapy, which is expected to be approved in mid-2021, is the first available causal therapeutic approach. Aim In collaboration with the German Society of Neuropediatrics (GNP), the Working Group of Pediatric Metabolic Disorders (APS), the German Society of Neurosurgery (DGNC) and the German Society of Pediatrics and Adolescent Medicine (DGKJ), the structural requirements and practical aspects in the preparation, implementation and follow-up of the treatment with eladocagene exuparvovec were elaborated. Discussion The present statement compiles the necessary framework conditions for a quality-assured administration of eladocagene exuparvovec. The treatment requires prehospital, inpatient and posthospital care by a multiprofessional team in a specialized and qualified treatment center. Patient follow-up is intended to contribute to knowledge-generating care. Due to lack of data on the therapeutic (long-term) effect as well as on advantages and disadvantages of the different stereotactic approaches, a structured follow-up plan and documentation in an appropriate, industry-independent registry are necessary.Hintergrund Der autosomal-rezessiv vererbte Defekt der aromatischen L‑Aminosäure-Decarboxylase (AADC) führt zu einem ausgeprägten, kombinierten Mangel an Dopamin, Serotonin und Katecholaminen. Das klinische Bild ist charakterisiert durch eine rumpfbetonte, muskuläre Hypotonie, verzögertes oder fehlendes Erreichen der motorischen Meilensteine und okulogyre Krisen ab dem Säuglingsalter. Der Erfolg der konventionellen, medikamentösen Behandlung ist besonders bei schweren Verläufen sehr limitiert. Mit der intrazerebralen Applikation von Eladocagene exuparvovec (Upstaza®), einer AAV2-basierten Gentherapie, deren Zulassung für Mitte 2021 erwartet wird, steht erstmals ein kausaler Therapieansatz zur Verfügung. Ziel In Zusammenarbeit mit der Gesellschaft für Neuropädiatrie (GNP), der Arbeitsgemeinschaft pädiatrischer Stoffwechselstörungen (APS), der Gesellschaft für Neurochirurgie (DGNC) und der Deutschen Gesellschaft für Kinder- und Jugendmedizin (DGKJ) wurden die Strukturvoraussetzungen und die praktischen Aspekte in der Vorbereitung, Durchführung und Nachsorge der Therapie mit Eladocagene exuparvovec erarbeitet. Diskussion Die vorliegende Stellungnahme stellt die notwendigen Rahmenbedingungen für eine qualitätsgesicherte Anwendung von Eladocagene exuparvovec zusammen. Die Behandlung erfordert eine prästationäre, stationäre und poststationäre Betreuung durch ein multiprofessionelles Team in einem spezialisierten und qualifizierten Therapiezentrum. Die Nachsorge der Patienten soll zu einer wissensgenerierenden Versorgung beitragen. Aufgrund von fehlenden Daten zur therapeutischen (Langzeit‑)Wirkung sowie zu Vor- und Nachteilen der verschiedenen stereotaktischen Prozeduren sind ein strukturierter Nachsorgeplan und die Erfassung in einem geeigneten, industrieunabhängigen Register notwendig

Monogenic variants in dystonia: an exome-wide sequencing study

Background Dystonia is a clinically and genetically heterogeneous condition that occurs in isolation (isolated dystonia), in combination with other movement disorders (combined dystonia), or in the context of multisymptomatic phenotypes (isolated or combined dystonia with other neurological involvement). However, our understanding of its aetiology is still incomplete. We aimed to elucidate the monogenic causes for the major clinical categories of dystonia. Methods For this exome-wide sequencing study, study participants were identified at 33 movement-disorder and neuropaediatric specialty centres in Austria, Czech Republic, France, Germany, Poland, Slovakia, and Switzerland. Each individual with dystonia was diagnosed in accordance with the dystonia consensus definition. Index cases were eligible for this study if they had no previous genetic diagnosis and no indication of an acquired cause of their illness. The second criterion was not applied to a subset of participants with a working clinical diagnosis of dystonic cerebral palsy. Genomic DNA was extracted from blood of participants and whole-exome sequenced. To find causative variants in known disorder-associated genes, all variants were filtered, and unreported variants were classified according to American College of Medical Genetics and Genomics guidelines. All considered variants were reviewed in expert round-table sessions to validate their clinical significance. Variants that survived filtering and interpretation procedures were defined as diagnostic variants. In the cases that went undiagnosed, candidate dystonia-causing genes were prioritised in a stepwise workflow. Findings We sequenced the exomes of 764 individuals with dystonia and 346 healthy parents who were recruited between June 1, 2015, and July 31, 2019. We identified causative or probable causative variants in 135 (19%) of 728 families, involving 78 distinct monogenic disorders. We observed a larger proportion of individuals with diagnostic variants in those with dystonia (either isolated or combined) with coexisting non-movement disorder-related neurological symptoms (100 [45%] of 222;excepting cases with evidence of perinatal brain injury) than in those with combined (19 [19%] of 98) or isolated (16 [4%] of 388) dystonia. Across all categories of dystonia, 104 (65%) of the 160 detected variants affected genes which are associated with neurodevelopmental disorders. We found diagnostic variants in 11 genes not previously linked to dystonia, and propose a predictive clinical score that could guide the implementation of exome sequencing in routine diagnostics. In cases without perinatal sentinel events, genomic alterations contributed substantively to the diagnosis of dystonic cerebral palsy. In 15 families, we delineated 12 candidate genes. These include IMPDH2, encoding a key purine biosynthetic enzyme, for which robust evidence existed for its involvement in a neurodevelopmental disorder with dystonia. We identified six variants in IMPDH2, collected from four independent cohorts, that were predicted to be deleterious de-novo variants and expected to result in deregulation of purine metabolism. Interpretation In this study, we have determined the role of monogenic variants across the range of dystonic disorders, providing guidance for the introduction of personalised care strategies and fostering follow-up pathophysiological explorations

Beta-ureidopropionase deficiency presenting with febrile status epilepticus

Beta-ureidopropionase is the third enzyme in the catabolic pathway of uracil and thymine. To date, only three other patients are reported with this inborn error of metabolism. We report the clinical presentation of a male patient who presented at the age of 4 months after an ALTE-like event (ALTE = acute life-threatening event) with febrile status epilepticus. Such a clinical presentation has not been reported before in this condition. Diagnosis was based on biochemical, enzymatic and molecular studies. MRI (magnetic resonance imaging) at the age of 11 months demonstrated large subdural hematomata and global supratentorial atrophy. At that time the patient showed severe psychomotor retardation with muscular hypotonia, extremely limited visual contact and poorly controlled epilepsy. CONCLUSIONS: Pyrimidine degradation defects should be included in the differential diagnosis of convulsions, (febrile) status epilepticus, psychomotor retardation and possibly also ALTE-like event

Genotype–phenotype correlation and treatment effects in young patients with GNAO1 -associated disorders

Background Patients carrying pathogenic variants in GNAO1 often present with early-onset central hypotonia and global developmental delay, with or without epilepsy. As the disorder progresses, a complex hypertonic and hyperkinetic movement disorder is a common phenotype. A genotype–phenotype correlation has not yet been described and there are no evidence-based therapeutic recommendations. Methods To improve understanding of the clinical course and pathophysiology of this ultra-rare disorder, we built up a registry for GNAO1 patients in Germany. In this retrospective, multicentre cohort study, we collected detailed clinical data, treatment effects and genetic data for 25 affected patients. Results The main clinical features were symptom onset within the first months of life, with central hypotonia or seizures. Within the first year of life, nearly all patients developed a movement disorder comprising dystonia (84%) and choreoathetosis (52%). Twelve (48%) patients suffered life-threatening hyperkinetic crises. Fifteen (60%) patients had epilepsy with poor treatment response. Two patients showed an atypical phenotype and seven novel pathogenic variants in GNAO1 were identified. Nine (38%) patients were treated with bilateral deep brain stimulation of the globus pallidus internus. Deep brain stimulation reduced hyperkinetic symptoms and prevented further hyperkinetic crises. The in silico prediction programmes did not predict the phenotype by the genotype. Conclusion The broad clinical spectrum and genetic findings expand the phenotypical spectrum of GNAO1 -associated disorder and therefore disprove the assumption that there are only two main phenotypes. No specific overall genotype–phenotype correlation was identified. We highlight deep brain stimulation as a useful treatment option in this disorder