bims-meglyc 2024-08-11 papers

Issue of 2024–08–11
four papers selected by
Silvia Radenkovic, UMC Utrecht

J Inherit Metab Dis. 2024 Aug 06.

Neurodevelopmental profiles of 14 individuals with phosphomannomutase deficiency (PMM2-CDG).

Tara Weixel, Dee Adedipe, Glennis Muldoon, Christina Lam, Donna Krasnewich, Audrey Thurm, Lynne Wolfe.

PMM2-CDG (formerly CDG-1a), the most common type of congenital disorders of glycosylation, is inherited in an autosomal recessive pattern. PMM2-CDG frequently presents in infancy with multisystemic clinical involvement, and it has been diagnosed in over 1000 people worldwide. There have been few natural history studies reporting neurodevelopmental characterization of PMM2-CDG. Thus, a prospective study was conducted that included neurodevelopmental assessments as part of deep phenotyping. This study, Clinical and Basic Investigations into Known and Suspected Congenital Disorders of Glycosylation (NCT02089789), included 14 participants (8 males and 6 females ages 2-33 years) with a confirmed molecular diagnosis of PMM2-CDG. Clinical features of PMM2-CDG in this cohort were neurodevelopmental disorders, faltering growth, hypotonia, cerebellar atrophy, peripheral neuropathy, movement disorders, ophthalmological abnormalities, and auditory function differences. All PMM2-CDG participants met criteria for intellectual disability (or global developmental delay if younger than age 5). The majority never attained certain gross motor and language milestones. Only two participants were ambulatory, and almost all were considered minimally verbal. Overall, individuals with PMM2-CDG present with a complex neurodevelopmental profile characterized by intellectual disability and multisystemic presentations. This systematic quantification of the neurodevelopmental profile of PMM2-CDG expands our understanding of the range in impairments associated with PMM2-CDG and will help guide management strategies.

Keywords: congenital disorders of glycosylation; intellectual disability; neurodevelopment; neuropsychological assessment; phosphomannomutase deficiency

DOI: https://doi.org/10.1002/jimd.12782

Mol Genet Metab. 2024 Jul 17. pii: S1096-7192(24)00422-0. [Epub ahead of print]143(1-2): 108538

HepG2 PMM2-CDG knockout model: A versatile platform for variant and therapeutic evaluation.

Alicia Vilas, Álvaro Briso-Montiano, Cristina Segovia-Falquina, Arturo Martín-Martínez, Alejandro Soriano-Sexto, Diana Gallego, Vera Ruiz-Montés, Alejandra Gámez, Belén Pérez.

Phosphomannomutase 2 deficiency (PMM2-CDG), the most frequent congenital disorder of glycosylation, is an autosomal recessive disease caused by biallelic pathogenic variants in the PMM2 gene. There is no cure for this multisystemic syndrome. Some of the therapeutic approaches that are currently in development include mannose-1-phosphate replacement therapy, drug repurposing, and the use of small chemical molecules to correct folding defects. Preclinical models are needed to evaluate the efficacy of treatments to overcome the high lethality of the available animal model. In addition, the number of variants with unknown significance is increasing in clinical settings. This study presents the generation of a cellular disease model by knocking out the PMM2 gene in the hepatoma HepG2 cell line using CRISPR-Cas9 gene editing. The HepG2 knockout model accurately replicates the PMM2-CDG phenotype, exhibiting a complete absence of PMM2 protein and mRNA, a 90% decrease in PMM enzymatic activity, and altered ICAM-1, LAMP1 and A1AT glycoprotein patterns. The evaluation of PMM2 disease-causing variants validates the model's utility for studying new PMM2 clinical variants, providing insights for diagnosis and potentially for evaluating therapies. A CRISPR-Cas9-generated HepG2 knockout model accurately recapitulates the PMM2-CDG phenotype, providing a valuable tool for assessing disease-causing variants and advancing therapeutic strategies.

Keywords: CRISPR-Cas9; Disease model; HepG2; Knockout; Phosphomannomutase 2 deficiency (PMM2-CDG); Therapeutic strategies; Variant evaluation

DOI: https://doi.org/10.1016/j.ymgme.2024.108538

J Biol Chem. 2024 Aug 02. pii: S0021-9258(24)02129-X. [Epub ahead of print] 107628

In vivo Mapping of the Mouse Galnt3-specific O-Glycoproteome.

Kruti Bhavik Dalal, Weiming Yang, E Tian, Aliona Chernish, Peggy McCluggage, Alexander J Lara, Kelly G Ten Hagen, Lawrence A Tabak.

The UDP-N-acetylgalactosamine polypeptide:N-acetylgalactosaminyltransferase (GalNAc-T) family of enzymes initiates O-linked glycosylation by catalyzing the addition of the first GalNAc sugar to serine or threonine on proteins destined to be membrane-bound or secreted. Defects in individual isoforms of the GalNAc-T family can lead to certain congenital disorders of glycosylation (CDG). The GALNT3-CDG, is caused by mutations in GALNT3, resulting in hyperphosphatemic familial tumoral calcinosis (HFTC) due to impaired glycosylation of the phosphate-regulating hormone FGF23 within osteocytes of the bone. Patients with hyperphosphatemia present altered bone density, abnormal tooth structure and calcified masses throughout the body. It is therefore important to identify all potential substrates of GalNAc-T3 throughout the body to understand the complex disease phenotypes. Here, we compared the Galnt3-/- mouse model, which partially phenocopies GALNT3-CDG, with wild-type mice and employed a multi-component approach utilizing chemoenzymatic conditions, a product-dependent method constructed using EThcD triggered scans in a mass spectrometry workflow, quantitative O-glycoproteomics, and global proteomics to identify 663 Galnt3-specific O-glycosites from 269 glycoproteins across multiple tissues. Consistent with the mouse and human phenotypes, functional networks of glycoproteins that contain GalNAc-T3-specific O-glycosites involved in skeletal morphology, mineral level maintenance and hemostasis were identified. This library of in vivo GalNAc-T3-specific substrate proteins and O-glycosites will serve as a valuable resource to understand the functional implications of O-glycosylation and to unravel the underlying causes of complex human GALNT3-CDG phenotypes.

Keywords: GalNAc-T; Galnt; Glycopeptides; Glycosyltransferase; Hyperphosphatemic Familial Tumoral Calcinosis (HFTC); O-GalNAc; O-glycosylation; mass spectrometry

DOI: https://doi.org/10.1016/j.jbc.2024.107628

Am J Med Genet A. 2024 Aug 09. e63833

Missense variant in PIGM associated with severe cystic encephalomalacia and portal vein thrombosis: Phenotypic and genotypic expansion of the glycosylphosphatidylinositol biosynthesis defect-1 (GPIBD1).

Lauren Brady, Rashmi Yadav, Andrew C Edmondson, Mark Tarnopolsky.

Glycosylphosphatidylinositols (GPIs) are a type of glycolipid responsible for anchoring many important proteins to the cell membrane surface. Defects in the synthesis of GPIs can lead to a group of multisystem disorders known as the inherited GPI deficiencies (IGDs). Homozygosity for the c.-270C > G variant in the promoter of PIGM has been associated with a IGD subtype known as glycosylphosphatidylinositol biosynthesis defect-1 (GPIBD1). The several cases reported in the literature have been described to have a milder neurologic phenotype in comparison to the other IGDs and have been treated with sodium phenylbutyrate with some degree of success. These patients typically present with portal and hepatic vein thrombosis and mostly develop absence seizures. Here we describe a patient homozygous for a nonsynonymous variant in PIGM who deceased at 9 weeks of life and had multiple physical dysmorphisms (rocker bottom feet, midline cleft palate, thickened and lichenified skin), portal vein thrombosis, CNS structural anomalies (progressive multicystic encephalomalacia and ventriculomegaly), and a neurological phenotype of a diffuse encephalopathy. This is the first known case report of a PIGM-related IGD/CDG due to a coding variant.

Keywords: PIGM; congenital disorders of glycosylation; glycosylphosphatidylinositol; inherited GPI deficiencies

DOI: https://doi.org/10.1002/ajmg.a.63833