Approximately 35 % of the mouse genes are indispensable for life, thus, global knock-out (KO) of those genes may result in embryonic or early postnatal lethality due to developmental abnormalities. Several KO mouse lines are valuable human disease models, but viable homozygous mutant mice are frequently required to mirror most symptoms of a human disease. The site-specific gene editing systems, the transcription activator-like effector nucleases (TALENs), Zinc-finger nucleases (ZFNs) and the clustered regularly interspaced short palindrome repeat-associated Cas9 nuclease (CRISPR/Cas9) made the generation of KO mice more efficient than before, but the homozygous lethality is still an undesired side-effect in case of many genes. The literature search was conducted using PubMed and Web of Science databases until June 30th, 2020. The following terms were combined to find relevant studies: "lethality", "mice", "knock-out", "deficient", "embryonic", "perinatal", "rescue". Additional manual search was also performed to find the related human diseases in the Online Mendelian Inheritance in Man (OMIM) database and to check the citations of the selected studies for rescuing methods. In this review, the possible solutions for rescuing human disease-relevant homozygous KO mice lethal phenotypes were summarized.

• MeSH
• CRISPR-Cas Systems genetics   MeSH
• Gene Editing methods   MeSH
• Phenotype MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Zinc Finger Nucleases genetics   MeSH
• Transcription Activator-Like Effector Nucleases genetics   MeSH
• Embryo Loss genetics   prevention & control   MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Zinc Finger Nucleases MeSH
• Transcription Activator-Like Effector Nucleases MeSH

Phosphoglucomutase 1 (PGM1) deficiency is a rare genetic disorder that affects glycogen metabolism, glycolysis, and protein glycosylation. Previously known as GSD XIV, it was recently reclassified as a congenital disorder of glycosylation, PGM1-CDG. PGM1-CDG usually manifests as a multisystem disease. Most patients present as infants with cleft palate, liver function abnormalities and hypoglycemia, but some patients present in adulthood with isolated muscle involvement. Some patients develop life-threatening cardiomyopathy. Unlike most other CDG, PGM1-CDG has an effective treatment option, d-galactose, which has been shown to improve many of the patients' symptoms. Therefore, early diagnosis and initiation of treatment for PGM1-CDG patients are crucial decisions. In this article, our group of international experts suggests diagnostic, follow-up, and management guidelines for PGM1-CDG. These guidelines are based on the best available evidence-based data and experts' opinions aiming to provide a practical resource for health care providers to facilitate successful diagnosis and optimal management of PGM1-CDG patients.

• Keywords
• d-galactose, PGM1-CDG, congenital disorder of glycosylation, management guidelines, phosphoglucomutase 1 deficiency,
• MeSH
• Adult MeSH
• Galactose therapeutic use   MeSH
• Glycogen Storage Disease complications   diagnosis   drug therapy   enzymology   MeSH
• Hypoglycemia complications   MeSH
• Cardiomyopathies complications   pathology   MeSH
• Infant MeSH
• Consensus MeSH
• Humans MeSH
• Disease Management * MeSH
• International Cooperation MeSH
• Muscular Diseases complications   pathology   MeSH
• Cleft Palate complications   pathology   MeSH
• Check Tag
• Adult MeSH
• Infant MeSH
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Research Support, N.I.H., Extramural MeSH
• Practice Guideline MeSH
• Names of Substances
• Galactose MeSH

Phosphoglucomutase 1 (PGM1) encodes the metabolic enzyme that interconverts glucose-6-P and glucose-1-P. Mutations in PGM1 cause impairment in glycogen metabolism and glycosylation, the latter manifesting as a congenital disorder of glycosylation (CDG). This unique metabolic defect leads to abnormal N-glycan synthesis in the endoplasmic reticulum (ER) and the Golgi apparatus (GA). On the basis of the decreased galactosylation in glycan chains, galactose was administered to individuals with PGM1-CDG and was shown to markedly reverse most disease-related laboratory abnormalities. The disease and treatment mechanisms, however, have remained largely elusive. Here, we confirm the clinical benefit of galactose supplementation in PGM1-CDG-affected individuals and obtain significant insights into the functional and biochemical regulation of glycosylation. We report here that, by using tracer-based metabolomics, we found that galactose treatment of PGM1-CDG fibroblasts metabolically re-wires their sugar metabolism, and as such replenishes the depleted levels of galactose-1-P, as well as the levels of UDP-glucose and UDP-galactose, the nucleotide sugars that are required for ER- and GA-linked glycosylation, respectively. To this end, we further show that the galactose in UDP-galactose is incorporated into mature, de novo glycans. Our results also allude to the potential of monosaccharide therapy for several other CDG.

• Keywords
• CDG, PGM1-CDG, central carbon metabolism, galactose, glycosylation, mitochondria, nucleotide sugars, tracer metabolomics,
• MeSH
• Fibroblasts drug effects   metabolism   pathology   MeSH
• Phosphoglucomutase deficiency   MeSH
• Galactose administration & dosage   MeSH
• Glycosylation MeSH
• Cohort Studies MeSH
• Cells, Cultured MeSH
• Humans MeSH
• Uridine Diphosphate Galactose metabolism   MeSH
• Uridine Diphosphate Glucose metabolism   MeSH
• Congenital Disorders of Glycosylation drug therapy   metabolism   pathology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Phosphoglucomutase MeSH
• Galactose MeSH
• Uridine Diphosphate Galactose MeSH
• Uridine Diphosphate Glucose MeSH

Phosphoglucomutase 1 (PGM1) deficiency results in a mixed phenotype of a Glycogen Storage Disorder and a Congenital Disorder of Glycosylation (CDG). Screening for abnormal glycosylation has identified more than 40 patients, manifesting with a broad clinical and biochemical spectrum which complicates diagnosis. Together with the availability of D-galactose as dietary therapy, there is an urgent need for specific glycomarkers for early diagnosis and treatment monitoring. We performed glycomics profiling by high-resolution QTOF mass spectrometry in a series of 19 PGM1-CDG patients, covering a broad range of biochemical and clinical severity. Bioinformatics and statistical analysis were used to select glycomarkers for diagnostics and define glycan-indexes for treatment monitoring. Using 3 transferrin glycobiomarkers, all PGM1-CDG patients were diagnosed with 100% specificity and sensitivity. Total plasma glycoprofiling showed an increase in high mannose glycans and fucosylation, while global galactosylation and sialylation were severely decreased. For treatment monitoring, we defined 3 glycan-indexes, reflecting normal glycosylation, a lack of complete glycans (LOCGI) and of galactose residues (LOGI). These indexes showed improved glycosylation upon D-galactose treatment with a fast and near-normalization of the galactose index (LOGI) in 6 out of 8 patients and a slower normalization of the LOCGI in all patients. Total plasma glycoprofiling showed improvement of the global high mannose glycans, fucosylation, sialylation, and galactosylation status on D-galactose treatment. Our study indicates specific glycomarkers for diagnosis of mildly and severely affected PGM1-CDG patients, and to monitor the glycan-specific effects of D-galactose therapy.

• MeSH
• Biomarkers blood   MeSH
• Early Diagnosis MeSH
• Child MeSH
• Adult MeSH
• Galactose therapeutic use   MeSH
• Glycogen Storage Disease blood   diagnosis   diet therapy   MeSH
• Glycosylation MeSH
• Mass Spectrometry MeSH
• Infant MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Monitoring, Physiologic MeSH
• Child, Preschool MeSH
• Sensitivity and Specificity MeSH
• Transferrin metabolism   MeSH
• Chromatography, High Pressure Liquid MeSH
• Check Tag
• Child MeSH
• Adult MeSH
• Infant MeSH
• Middle Aged MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Child, Preschool MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Biomarkers MeSH
• Galactose MeSH
• Transferrin MeSH

N-methyl-D-aspartate receptors (NMDARs) play critical roles in both excitatory neurotransmission and synaptic plasticity. NMDARs containing the nonconventional GluN3A subunit have different functional properties compared to receptors comprised of GluN1/GluN2 subunits. Previous studies showed that GluN1/GluN2 receptors are regulated by N-glycosylation; however, limited information is available regarding the role of N-glycosylation in GluN3A-containing NMDARs. Using a combination of microscopy, biochemistry, and electrophysiology in mammalian cell lines and rat hippocampal neurons, we found that two asparagine residues (N203 and N368) in the GluN1 subunit and three asparagine residues (N145, N264 and N275) in the GluN3A subunit are required for surface delivery of GluN3A-containing NMDARs. Furthermore, deglycosylation and lectin-based analysis revealed that GluN3A subunits contain extensively modified N-glycan structures, including hybrid/complex forms of N-glycans. We also found (either using a panel of inhibitors or by studying human fibroblasts derived from patients with a congenital disorder of glycosylation) that N-glycan remodeling is not required for the surface delivery of GluN3A-containing NMDARs. Finally, we found that the surface mobility of GluN3A-containing NMDARs in hippocampal neurons is increased following incubation with 1-deoxymannojirimycin (DMM, an inhibitor of the formation of the hybrid/complex forms of N-glycans) and decreased in the presence of specific lectins. These findings provide new insight regarding the mechanisms by which neurons can regulate NMDAR trafficking and function.

• Keywords
• endoplasmic reticulum, excitatory synapse, glutamate receptor, glycan, ion channel, mammalian neuron,
• Publication type
• Journal Article MeSH

PurposePhosphoglucomutase-1 deficiency is a subtype of congenital disorders of glycosylation (PGM1-CDG). Previous casereports in PGM1-CDG patients receiving oral D-galactose (D-gal) showed clinical improvement. So far no systematic in vitro and clinical studies have assessed safety and benefits of D-gal supplementation. In a prospective pilot study, we evaluated the effects of oral D-gal in nine patients.MethodsD-gal supplementation was increased to 1.5 g/kg/day (maximum 50 g/day) in three increments over 18 weeks. Laboratory studies were performed before and during treatment to monitor safety and effect on serum transferrin-glycosylation, coagulation, and liver and endocrine function. Additionally, the effect of D-gal on cellular glycosylation was characterized in vitro.ResultsEight patients were compliant with D-gal supplementation. No adverse effects were reported. Abnormal baseline results (alanine transaminase, aspartate transaminase, activated partial thromboplastin time) improved or normalized already using 1 g/kg/day D-gal. Antithrombin-III levels and transferrin-glycosylation showed significant improvement, and increase in galactosylation and whole glycan content. In vitro studies before treatment showed N-glycan hyposialylation, altered O-linked glycans, abnormal lipid-linked oligosaccharide profile, and abnormal nucleotide sugars in patient fibroblasts. Most cellular abnormalities improved or normalized following D-gal treatment. D-gal increased both UDP-Glc and UDP-Gal levels and improved lipid-linked oligosaccharide fractions in concert with improved glycosylation in PGM1-CDG.ConclusionOral D-gal supplementation is a safe and effective treatment for PGM1-CDG in this pilot study. Transferrin glycosylation and ATIII levels were useful trial end points. Larger, longer-duration trials are ongoing.

• MeSH
• Administration, Oral MeSH
• Child MeSH
• Phosphoglucomutase metabolism   MeSH
• Galactose administration & dosage   adverse effects   therapeutic use   MeSH
• Glycogen Storage Disease drug therapy   MeSH
• Glycoproteins metabolism   MeSH
• Blood Coagulation MeSH
• Infant MeSH
• Creatine Kinase blood   MeSH
• Blood Glucose metabolism   MeSH
• Skin cytology   metabolism   MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Pilot Projects MeSH
• Child, Preschool MeSH
• Prospective Studies MeSH
• Transferrin metabolism   MeSH
• Dose-Response Relationship, Drug MeSH
• Check Tag
• Child MeSH
• Infant MeSH
• Humans MeSH
• Adolescent MeSH
• Young Adult MeSH
• Male MeSH
• Child, Preschool MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Clinical Trial MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Phosphoglucomutase MeSH
• Galactose MeSH
• Glycoproteins MeSH
• Creatine Kinase MeSH
• Blood Glucose MeSH
• PGM1 protein, human MeSH Browser
• Transferrin MeSH