Pathogenic DPAGT1 variants in limb-girdle congenital myasthenic syndrome (LG-CMS) associated with tubular aggregates and ORAI1 hypoglycosylation

Laura Vanden Brande; Stéphanie Bauché; Laura Pérez-Guàrdia; Damien Sternberg; Andreea M Seferian; Edoardo Malfatti; Roberto Silva-Rojas; Clémence Labasse; Frédéric Chevessier; Pierre Carlier; Bruno Eymard; Norma B Romero; Jocelyn Laporte; Laurent Servais; Teresa Gidaro; Johann Böhm

doi:10.1111/nan.12952

Pathogenic DPAGT1 variants in limb-girdle congenital myasthenic syndrome (LG-CMS) associated with tubular aggregates and ORAI1 hypoglycosylation

Neuropathol Appl Neurobiol. 2023 Dec 20:e12952. doi: 10.1111/nan.12952. Online ahead of print.

Authors

Laura Vanden Brande^{1

2}, Stéphanie Bauché^{1

3}, Laura Pérez-Guàrdia⁴, Damien Sternberg⁵, Andreea M Seferian², Edoardo Malfatti^{1

6}, Roberto Silva-Rojas⁴, Clémence Labasse¹, Frédéric Chevessier¹, Pierre Carlier¹, Bruno Eymard^{1

6}, Norma B Romero¹, Jocelyn Laporte⁴, Laurent Servais^{7

8}, Teresa Gidaro^{1

2}, Johann Böhm⁴

Affiliations

¹ Institut de Myologie, GHU La Pitié-Salpêtrière, Paris, France.
² Assistance Publique Hôpitaux de Paris, Sorbonne Université, Institut de Myologie, AFM-Téléthon, Essais cliniques I-Motion Enfants, Hôpital Armand Trousseau, Paris, France.
³ Inserm U 1127, CNRS UMR 7225, Sorbonne Universités, UPMC Université Paris 06 UMR S 1127, Institut du Cerveau et de la Moelle épinière, ICM, Paris, France.
⁴ Departement of Translational Medicine and Neurogenetics, IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Inserm U1258, CNRS UMR7104, Université de Strasbourg, Illkirch, France.
⁵ Service de Biochimie Métabolique, UF Cardiogenetics and Myogenetics, Hôpital de la Pitié-Salpêtrière, APHP, Paris, France.
⁶ Centre de Référence de Pathologie Neuromusculaire Paris-Est, Groupe Hospitalier Pitié-Salpêtrière, Paris, France.
⁷ MDUK Oxford Neuromuscular Centre & NIHR Oxford Biomedical Research Centre, University of Oxford, Oxford, UK.
⁸ Neuromuscular Reference Center, Department of Paediatrics, University and University Hospital of Liege, Belgium.

PMID: 38124360
DOI: 10.1111/nan.12952

Abstract

Aims: Limb-girdle congenital myasthenic syndrome (LG-CMS) is a genetically heterogeneous disorder characterized by muscle weakness and fatigability. The LG-CMS gene DPAGT1 codes for an essential enzyme of the glycosylation pathway, a posttranslational modification mechanism shaping the structure and function of proteins. In DPAGT1-related LG-CMS, reduced glycosylation of the acetylcholine receptor (AChR) reduces its localization at the neuromuscular junction (NMJ), and results in diminished neuromuscular transmission. LG-CMS patients also show tubular aggregates on muscle biopsy, but the origin and potential contribution of the aggregates to disease development are not understood. Here, we describe two LG-CMS patients with the aim of providing a molecular diagnosis and to shed light on the pathways implicated in tubular aggregate formation.

Methods: Following clinical examination of the patients, we performed next-generation sequencing (NGS) to identify the genetic causes, analysed the biopsies at the histological and ultrastructural levels, investigated the composition of the tubular aggregates, and performed experiments on protein glycosylation.

Results: We identified novel pathogenic DPAGT1 variants in both patients, and pyridostigmine treatment quantitatively improved muscle force and function. The tubular aggregates contained proteins of the sarcoplasmic reticulum (SR) and structurally conformed to the aggregates observed in tubular aggregate myopathy (TAM). TAM arises from overactivation of the plasma membrane calcium channel ORAI1, and functional studies on muscle extracts from our LG-CMS patients evidenced abnormal ORAI1 glycosylation.

Conclusions: We expand the genetic variant spectrum of LG-CMS and provide a genotype/phenotype correlation for pathogenic DPAGT1 variants. The discovery of ORAI1 hypoglycosylation in our patients highlights a physiopathological link between LG-CMS and TAM.

Keywords: DPAGT1; LG-CMS; Limb-girdle congenital myasthenic syndrome; ORAI1; glycosylation; tubular aggregates.