Similarity of Phenotype in Three Male Patients With the c.320A>G Variant in ALG13: Possible Genotype-Phenotype Correlation.

BACKGROUND: Congenital disorders of glycosylation (CDG) are a group of neurometabolic diseases that result from genetic defects in the glycosylation of proteins and/or lipids. Multiple pathogenic genes contribute to the varying reported phenotypes of individuals with CDG-1 syndromes, most of which are inherited as autosomal recessive traits, although X-linked inheritance has also been reported. Pathogenic variants in the asparagine-linked glycosylation 13 homolog (ALG13) gene have been implicated in the aetiology of developmental and epileptic encephalopathy (DEE) 36 (OMIM:*300776, DEE36). The NM_001099922.3:c.320A>G; p.(Asn107Ser) variant is the most frequently described pathogenic variant in ALG13, with 59 females and 2 males with this variant reported to date. METHODS: We report on a male with a de novo, hemizygous variant in ALG13: c.320A>G; p.(Asn107Ser), whose phenotype resembles that of two previously reported males with the same variant. RESULTS: All three males have a de novo mutation, infantile spasms, DEE, drug-resistant epilepsy, intellectual disability, dysmorphic findings, recurrent infections, skeletal anomalies, brain abnormalities and a movement disorder: a phenotype not consistently reported in males with other pathogenic variants in ALG13. CONCLUSION: The similarity of phenotype in the three males with the c.320A>G variant in ALG13, suggests a possible genotype-phenotype correlation.

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.

The trap of genetic tag: The importance of pathogenicity prediction tools in the correct interpretation of variants of uncertain significance in the era of high-throughput genome sequencing.

Although recent advancements in DNA sequencing technologies and their widely used, the interpretation of variants of uncertain significance from these large datasets is not clear-cut. Here, we present the case of a family referred to our metabolic disease department, in which three males' individuals were affected by a suspected a genetic inherited disease, resulting from next-generation sequencing results. A correct assessment of the clinical significance of the genetic variant found in our cases, with a review of the literature, the evaluation of population database and the use of computational predictive program changed the initial suspect. Despite NGS technologies have increased diagnostic sensitivity, most of these variants remains of uncertain clinical significance. An efficient systematic approach is fundamental to determine the pathogenicity of a variant, avoiding incorrect interpretation in a clinical setting.

Long-term outcomes in ALG13-Congenital Disorder of Glycosylation.

ALG13-CDG is a rare X-linked disorder of N-linked glycosylation. Given the lack of long-term outcome data in ALG13-CDG, we collected natural history data and reviewed individuals surviving to young adulthood with confirmed pathogenic variants in ALG13 in our own cohort and in the literature. From the 14 ALG13-CDG patients enrolled into our Frontiers of Congenital Disorders of Glycosylation Consortium natural history study only two patients were older than 16 years; one of these two females is so far unreported. From the 52 patients described in the medical literature with confirmed pathogenic variants in ALG13 only five patients were older than 16 years (all females), in addition to the new, unreported patient from our natural history study. Two male patients have died due to ALG13-CDG, and there were no surviving males older than 16 years with a confirmed ALG13-CDG diagnosis. Our adolescent and young adult cohort of six patients presented with epilepsy, muscular hypotonia, speech, and developmental delay. Intellectual disability was present in all female patients with ALG13-CDG. Unreported features included ataxia, neuropathy, and severe gastrointestinal symptoms requiring G/J tube placement. In addition, two patients from our natural history study developed unilateral hearing loss. Skeletal abnormalities were found in four patients, including osteopenia and scoliosis. Major health problems included persistent seizures in three patients. Ketogenic diet was efficient for seizures in three out of four patients. Although all patients were mobile, they all had severe communication problems with mostly absent speech and were unable to function without parental support. In summary, long-term outcome in ALG13-CDG includes gastrointestinal and skeletal involvement in addition to a chronic, mostly non-progressive neurologic phenotype.

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.

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.

ALG13-CDG with Infantile Spasms in a Male Patient Due to a De Novo ALG13 Gene Mutation.

A boy presented at the age of 3.5 months with a developmental delay. He developed infantile spasms with hypsarrhytmia on EEG 1 month later. Additional symptoms were delayed visual development, asymmetrical hearing loss, hypotonia, and choreoathetoid movements. He also had some dysmorphic features and was vulnerable for infections. He was treated successively with vigabatrin, prednisolone, valproic acid, nitrazepam, and lamotrigine without a lasting clinical effect, but showed a treatment response to levetiracetam. Cerebral MRI showed hypoplasia of the corpus callosum and a mild delay in myelination. Further investigations including metabolic screening and glycosylation studies by transferrin isoelectric focusing were all considered to be normal. Whole-exome sequencing identified a de novo mutation in the ALG13 gene (c.320A>G, p.(Asn107Ser)). Mutations in this gene, which is located on the X-chromosome, are associated with congenital disorders of glycosylation type I (CDG-I). Mass spectrometric analysis of transferrin showed minor glycosylation abnormalities. The c.320A>G mutation in ALG13 has until now only been described in girls and was thought to be lethal for boys. All girls with this specific mutation presented with a similar phenotype of developmental delay and severe early onset epilepsy. In two girls glycosylation studies were performed which showed a normal glycosylation pattern. This is the first boy presenting with an epileptic encephalopathy caused by the c.320A>G mutation in the ALG13 gene. Since glycosylation studies are near-normal in patients with this mutation, the diagnosis of ALG13-CDG can be missed if genetic studies are not performed.