X-Linked ALG13 Gene Variant as a Cause of Epileptic Encephalopathy in Girls

ALG13-Congenital Disorder of Glycosylation (ALG13-CDG): Updated clinical and molecular review and clinical management guidelines

ALG13-Congenital Disorder of Glycosylation (CDG), is a rare X-linked CDG caused by pathogenic variants in ALG13 (OMIM 300776) that affects the N-linked glycosylation pathway. Affected individuals present with a predominantly neurological manifestation during infancy. Epileptic spasms are a common presenting symptom of ALG13-CDG. Other common phenotypes include developmental delay, seizures, intellectual disability, microcephaly, and hypotonia. Current management of ALG13-CDG is targeted to address patients' symptoms. To date, less than 100 individuals have been reported with ALG13-CDG. In this article, an international group of experts in CDG reviewed all reported individuals affected with ALG13-CDG and suggested diagnostic and management guidelines for ALG13-CDG. The guidelines are based on the best available data and expert opinion. Neurological symptoms dominate the phenotype of ALG13-CDG where epileptic spasm is confirmed to be the most common presenting symptom of ALG13-CDG in association with hypotonia and developmental delay. We propose that ACTH/prednisolone treatment should be trialed first, followed by vigabatrin, however ketogenic diet has been shown to have promising results in ALG13-CDG. In order to optimize medical management, we also suggest early cardiac, gastrointestinal, skeletal, and behavioral assessments in affected patients.

Delineating the epilepsy phenotype of NRROS-related microgliopathy: A case report and literature review

BACKGROUND

Negative regulator of reactive oxygen species (NRROS) related microgliopathy, a rare and recently recognized neurodegenerative condition, is caused by pathogenic variants in the NRROS gene, which plays a major role in the regulation of transforming growth factor-beta 1.

METHODS

We report a child presenting with infantile spasms syndrome (ISS) with subsequent progressive neurodegeneration who was identified to harbour a novel likely pathogenic NRROS variant (c.1359del; p.Ser454Alafs*11). The previously published reports of patients with this disorder were also reviewed systematically.

RESULTS

Including our index patient, 11 children (6 girls) were identified in total. Early development was normal in seven of these eleven children. All had a history of drug-resistant epilepsy, with 3 having epileptic spasms. The median age at seizure onset and developmental regression was 12 months, and the median age at death was 36 months. Intracranial calcifications were described in eight of eleven children. Neuroimaging revealed progressive cerebral atrophy and white matter loss in all children. The most common reported genetic variation was c.1981delC; (p.Leu661Serfs*97) observed in two families (likely due to a founder effect).

CONCLUSIONS

Pathogenic variants in NRROS should be suspected in children with neuro-regression and drug-resistant epilepsy including ISS with onset in the first two years of life. Punctate or serpiginous calcifications at the grey-white matter junction and acquired microcephaly are further clues towards the diagnosis.

Structural Analysis of the Effect of Asn107Ser Mutation on Alg13 Activity and Alg13-Alg14 Complex Formation and Expanding the Phenotypic Variability of ALG13-CDG

Congenital Disorders of Glycosylation (CDG) are multisystemic metabolic disorders showing highly heterogeneous clinical presentation, molecular etiology, and laboratory results. Here, we present different transferrin isoform patterns (obtained by isoelectric focusing) from three female patients harboring the ALG13 c.320A>G mutation. Contrary to other known variants of type I CDGs, where transferrin isoelectric focusing revealed notably increased asialo- and disialotransferrin fractions, a normal glycosylation pattern was observed in the probands. To verify this data and give novel insight into this variant, we modeled the human Alg13 protein and analyzed the dynamics of the apo structure and the complex with the UDP-GlcNAc substrate. We also modeled the Alg13-Alg14 heterodimer and ran multiple simulations of the complex in the presence of the substrate. Finally, we proposed a plausible complex formation mechanism.

ALG13 X-linked intellectual disability: New variants, glycosylation analysis, and expanded phenotypes

Pathogenic variants in ALG13 (ALG13 UDP-N-acetylglucosaminyltransferase subunit) cause an X-linked congenital disorder of glycosylation (ALG13-CDG) where individuals have variable clinical phenotypes that include developmental delay, intellectual disability, infantile spasms, and epileptic encephalopathy. Girls with a recurrent de novo c.3013C>T; p.(Asn107Ser) variant have normal transferrin glycosylation. Using a highly sensitive, semi-quantitative flow injection-electrospray ionization-quadrupole time-of-flight mass spectrometry (ESI-QTOF/MS) N-glycan assay, we report subtle abnormalities in N-glycans that normally account for <0.3% of the total plasma glycans that may increase up to 0.5% in females with the p.(Asn107Ser) variant. Among our 11 unrelated ALG13-CDG individuals, one male had abnormal serum transferrin glycosylation. We describe seven previously unreported subjects including three novel variants in ALG13 and report a milder neurodevelopmental course. We also summarize the molecular, biochemical, and clinical data for the 53 previously reported ALG13-CDG individuals. We provide evidence that ALG13 pathogenic variants may mildly alter N-linked protein glycosylation in both female and male subjects, but the underlying mechanism remains unclear.

Safety, Feasibility and Effectiveness of Pulse Methylprednisolone Therapy in Comparison with Intramuscular Adrenocorticotropic Hormone in Children with West Syndrome

OBJECTIVE

To assess the feasibility, effectiveness, and safety of pulse methylprednisolone in comparison with intramuscular adrenocorticotropic hormone (ACTH) therapy in children with West syndrome (WS).

METHODS

This open-label, pilot study with a parallel-group assignment included 44 recently diagnosed children with WS. Methylprednisolone therapy was given as intravenous infusion at a dose of 30 mg/kg/d for five days followed by oral steroids 1 mg/kg gradually tapered over 5-6 wk. The efficacy outcomes included a cessation of epileptic spasms (as per caregiver reporting) and resolution of hypsarrhythmia on electroencephalogram; safety outcome was the frequency of various adverse effects.

RESULTS

By day 14 of therapy, 6/18 (33.3%) children in the methylprednisolone group and 10/26 (38.5%) children in the ACTH group achieved cessation of epileptic spasms [group difference - 5.2%; confidence interval (CI) -30.7 to 22.8; p = 0.73]. However, by six weeks of therapy, 4/18 (22.2%) children in the methylprednisolone group and 11/26 (42.3%) children in the ACTH group had cessation of epileptic spasms (group difference - 20.1%; CI -43.0 to 8.4; p = 0.17). Hypertension was more commonly observed in the ACTH group (10 children) than in the methylprednisolone group (2 children; p = 0.046). Pulse methylprednisolone therapy was relatively safe.

CONCLUSIONS

The study observed limited effectiveness of both ACTH and pulse methylprednisolone therapy, which may partially be due to preponderance of structural etiology and a long treatment lag. However, pulse methylprednisolone therapy appeared to be safe, tolerable, and feasible for management of WS.

The First Metabolome Analysis in Children with Epilepsy and ALG13-CDG Resulting from c.320A>G Variant

BACKGROUND

ALG13-CDG belongs to the congenital disorders of glycosylation (CDG), which is an expanding group of multisystemic metabolic disorders caused by the N-linked, O-linked oligosaccharides, shared substrates, glycophosphatidylinositol (GPI) anchors, and dolichols pathways with high genetic heterogeneity. Thus, as far as clinical presentation, laboratory findings, and treatment are concerned, many questions are to be answered. Three individuals presented here may serve as a good example of clinical heterogeneity. This manuscript describes the first metabolomic analysis using NMR in three patients with epileptic encephalopathy due to the recurrent c.320A>G variant in ALG13, characterized to date only in about 60 individuals (mostly female). This is an important preliminary step in the understanding of the pathogenesis of the disease associated with this variant in the rare genetic condition. The disease is assumed to be a disorder of N-glycosylation given that this is the only known function of the ALG13 protein. Despite this, protein electrophoresis, which is abnormal in most conditions due to abnormalities in N-glycosylation, has been normal or only mildly abnormal in the ALG13 patients.

METHODS

Nuclear magnetic resonance (NMR) spectroscopy in conjunction with multivariate and univariate modelling were used to analyze the metabolic profile of the blood serum samples acquired from the studied patients.

RESULTS

Three metabolites were identified as potential biomarkers: betaine, N-acetyl-glycoprotein, and carnitine.

CONCLUSIONS

Since presented data are the first to be collected so far, they need be verified in further studies. Our intention was to turn attention toward possible CDG-ALG13 laboratory markers that would have clinical significance.

The phenotypic spectrum of X-linked, infantile onset ALG13-related developmental and epileptic encephalopathy

Objective

Asparagine‐linked glycosylation 13 (ALG13) deficiencies have been repeatedly described in the literature with the clinical phenotype of a developmental and epileptic encephalopathy (DEE). Most cases were females carrying the recurrent ALG13 de novo variant, p.(Asn107Ser), with normal transferrin electrophoresis.

Methods

We delineate the phenotypic spectrum of 38 individuals, 37 girls and one boy, 16 of them novel and 22 published, with the most common pathogenic ALG13 variant p.(Asn107Ser) and additionally report the phenotype of three individuals carrying other likely pathogenic ALG13 variants.

Results

The phenotypic spectrum often comprised pharmacoresistant epilepsy with epileptic spasms, mostly with onset within the first 6 months of life and with spasm persistence in one‐half of the cases. Tonic seizures were the most prevalent additional seizure type. Electroencephalography showed hypsarrhythmia and at a later stage of the disease in one‐third of all cases paroxysms of fast activity with electrodecrement. ALG13‐related DEE was usually associated with severe to profound developmental delay; ambulation was acquired by one‐third of the cases, whereas purposeful hand use was sparse or completely absent. Hand stereotypies and dyskinetic movements including dystonia or choreoathetosis were relatively frequent. Verbal communication skills were absent or poor, and eye contact and pursuit were often impaired.

Significance

X‐linked ALG13‐related DEE usually manifests as West syndrome with severe to profound developmental delay. It is predominantly caused by the recurrent de novo missense variant p.(Asn107Ser). Comprehensive functional studies will be able to prove or disprove an association with congenital disorder of glycosylation.

Predominant and novel de novo variants in 29 individuals with ALG13 deficiency: Clinical description, biomarker status, biochemical analysis, and treatment suggestions

Asparagine-linked glycosylation 13 homolog (ALG13) encodes a nonredundant, highly conserved, X-linked uridine diphosphate (UDP)-N-acetylglucosaminyltransferase required for the synthesis of lipid linked oligosaccharide precursor and proper N-linked glycosylation. De novo variants in ALG13 underlie a form of early infantile epileptic encephalopathy known as EIEE36, but given its essential role in glycosylation, it is also considered a congenital disorder of glycosylation (CDG), ALG13-CDG. Twenty-four previously reported ALG13-CDG cases had de novo variants, but surprisingly, unlike most forms of CDG, ALG13-CDG did not show the anticipated glycosylation defects, typically detected by altered transferrin glycosylation. Structural homology modeling of two recurrent de novo variants, p.A81T and p.N107S, suggests both are likely to impact the function of ALG13. Using a corresponding ALG13-deficient yeast strain, we show that expressing yeast ALG13 with either of the highly conserved hotspot variants rescues the observed growth defect, but not its glycosylation abnormality. We present molecular and clinical data on 29 previously unreported individuals with de novo variants in ALG13. This more than doubles the number of known cases. A key finding is that a vast majority of the individuals presents with West syndrome, a feature shared with other CDG types. Among these, the initial epileptic spasms best responded to adrenocorticotropic hormone or prednisolone, while clobazam and felbamate showed promise for continued epilepsy treatment. A ketogenic diet seems to play an important role in the treatment of these individuals.