Congenital disorders of glycosylation (CDG) are a group of metabolic disorders related to dysfunctional glycoprotein and glycolipid biosynthesis. ALG11-related CDG is a rare member of this group, characterized by severe neurodevelopmental impairment, progressive microcephaly, sensorineural hearing loss, and epilepsy. The objective of this report is to provide an update on the phenotype and brain magnetic resonance imaging (MRI) at age seven years for a patient initially described in early infancy with fetal brain disruption sequence. We provide an updated detailed clinical description of a seven-year-old male with ALG-11 CDG who underwent brain MRI at age seven years. Brain MRI at age seven years showed significant disease progression compared to the neonatal brain MRI. There was near complete loss of cerebral hemispheres, severe cerebellar atrophy, and decreased volume of the brainstem. The prior brain MRI (done at six weeks of age) had shown severe supratentorial volume loss but a relatively preserved cerebellum and brainstem at that time. Reports on the natural history of rare conditions are important to improve our understanding of these conditions. ALG11-CDG is associated with atrophy and eventual vanishing of supratentorial brain structures, and infratentorial brain structures later in the disease process. The involvement of a pediatric palliative care service is a valuable adjunct to assist with symptom management and family support for these complex progressive conditions.

Congenital disorders of glycosylation type 1p, one of the N-glycosylation defects, Asparagine-dependent glycosylation 11 (ALG11-CDG, #OMIM: 613,666), is a very rare type of autosomal recessive glycosylation defect that causes multisystem involvement and frequently presents with neurological symptoms such as epilepsy and neuromotor developmental delay. In this study, we aimed to present three Turkish patients from three unrelated families with the recurrent variant in the ALG11 gene, along with their clinical and genotypic findings, and to compare them with other cases described in the literature. Three patients from three unrelated families were identified who were comprehensively evaluated with clinical examination, laboratory tests, and imaging studies. The whole exome sequencing (WES) with copy number analysis was performed. The identified variants were confirmed in the proband and parents using Sanger sequencing. Common clinical features of the patients included refractory epileptic seizures, developmental delay, and microcephaly, consistent with the literature. Developmental and Epileptic Encephalopathy starting in the first year of life and burst suppression pattern observed in electroencephalogram are among the important clinical features. WES analysis revealed a homozygous NM_001004127.3: c.953A > C (p. Gln318Pro) missense variant in the ALG11 gene in all three patients. This study presents the clinical and genetic features of three Turkish patients with the ALG11-CDG subtype, which has been previously described in the literature; it reinforces the current knowledge on phenotypic diversity by comparisons with similar cases. In addition, the role of WES in the diagnosis of rare CDG subtypes has been demonstrated once again.

Congenital disorders of glycosylation (CDG) represent a heterogeneous group of rare inherited metabolic disorders due to abnormalities in protein or lipid glycosylation pathways, affecting multiple systems, and frequently being accompanied by neurological symptoms. ALG11-CDG, also known as CDG-1p, arises from a deficiency in a specific mannosyltransferase encoded by the ALG11 gene. To date, only 17 cases have been documented, and these patients have prominent clinical phenotypes, including seizures, developmental delay, and microcephaly. We describe a novel case of a four-month-old boy from a Chinese family exhibiting developmental delay, seizures, and microcephaly. Trio whole-exome sequencing (WES) and subsequent Sanger sequencing were employed to identify the potential genetic cause, and functional study was performed to evaluate the pathogenicity of genetic variant identified. Trio WES unveiled novel compound heterozygous variants: c.1307G>T (p.G436V) and c.1403G>A (p.R468H) within exon 4 of the ALG11 gene, inherited from the father and mother, respectively. Subsequent in vitro functional analysis revealed decreased stability of the mutant protein and concurrent hypoglycosylation of GP130, a hyperglycosylated protein. Our findings not only expand the clinical and variant spectrum of ALG11-CDG, but also emphasize the importance of WES as a first-tier genetic test in determining the molecular diagnosis.

Phosphomannomutase 2 (PMM2) converts mannose-6-phospahate to mannose-1-phosphate; the substrate for GDP-mannose, a building block of the glycosylation biosynthetic pathway. Pathogenic variants in the PMM2 gene have been shown to be associated with protein hypoglycosylation causing PMM2-congenital disorder of glycosylation (PMM2-CDG). While mannose supplementation improves glycosylation in vitro, but not in vivo, we hypothesized that liposomal delivery of mannose-1-phosphate could increase the stability and delivery of the activated sugar to enter the targeted compartments of cells. Thus, we studied the effect of liposome-encapsulated mannose-1-P (GLM101) on global protein glycosylation and on the cellular proteome in skin fibroblasts from individuals with PMM2-CDG, as well as in individuals with two N-glycosylation defects early in the pathway, namely ALG2-CDG and ALG11-CDG. We leveraged multiplexed proteomics and N-glycoproteomics in fibroblasts derived from different individuals with various pathogenic variants in PMM2, ALG2 and ALG11 genes. Proteomics data revealed a moderate but significant change in the abundance of some of the proteins in all CDG fibroblasts upon GLM101 treatment. On the other hand, N-glycoproteomics revealed the GLM101 treatment enhanced the expression levels of several high-mannose and complex/hybrid glycopeptides from numerous cellular proteins in individuals with defects in PMM2 and ALG2 genes. Both PMM2-CDG and ALG2-CDG exhibited several-fold increase in glycopeptides bearing Man6 and higher glycans and a decrease in Man5 and smaller glycan moieties, suggesting that GLM101 helps in the formation of mature glycoforms. These changes in protein glycosylation were observed in all individuals irrespective of their genetic variants. ALG11-CDG fibroblasts also showed increase in high mannose glycopeptides upon treatment; however, the improvement was not as dramatic as the other two CDG. Overall, our findings suggest that treatment with GLM101 overcomes the genetic block in the glycosylation pathway and can be used as a potential therapy for CDG with enzymatic defects in early steps in protein N-glycosylation.

Asparagine-dependent glycosylation 11-congenital disorders of glycosylation (ALG11-CDG) is a rare autosomal recessive N-glycosylation defect with multisystem involvement particularly neurological symptoms such as epilepsy and neuromotor developmental delay. A 31-month-old male patient admitted to our center with complaints of axial hypotonia, drug-resistant myoclonic seizures, microcephaly and deafness. The electroencephalography (EEG) showed a burst-suppression pattern without hypsarrhythmia. Basal metabolic investigations were unremarkable. Progressive cerebral atrophy, hypomyelination and corpus callosum hypoplasia were striking features in brain MRI images taken during our follow-up. Compound heterozygous mutations of the ALG11 gene were found by whole exome sequencing (WES) analysis. It was determined that the c.476T>C mutation is a novel mutation. CDG type 1 pattern was detected with the examination of carbohydrate-deficient transferrin (CDT) by capillary zone electrophoresis. In patients with a possible congenital defect of glycosylation, a screening test such as CDT analysis is suggested. To discover novel mutations in this rare disease group, expanded genetic analysis should be performed.