POPDC3 Gene Variants Associate with a New Form of Limb Girdle Muscular Dystrophy

Ann Neurol. 2019 Dec;86(6):832-843. doi: 10.1002/ana.25620.

John Vissing ¹, Katherine Johnson ² ³, Ana Töpf ², Shahriar Nafissi ⁴, Jordi Díaz-Manera ⁵, Vanessa M French ⁶, Roland F Schindler ⁶, Padmini Sarathchandra ⁷, Nicoline Løkken ¹, Susanne Rinné ⁸, Max Freund ⁸, Niels Decher ⁸, Thomas Müller ⁹, Morten Duno ¹⁰, Thomas Krag ¹, Thomas Brand ⁶, Volker Straub ² ³

Affiliations

1 Copenhagen Neuromuscular Center, Rigshospitalet, University of Copenhagen, Denmark.
2 John Walton Muscular Dystrophy Research Centre, Institute of Genetic Medicine, Newcastle University and Newcastle Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom.
3 Institute of Cellular Medicine, Newcastle University, Newcastle upon Tyne, United Kingdom.
4 Department of Neurology, Iranian Center of Neurological Research, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
5 Unitat de Malalties Neuromusculars, Servei de Neurologia, Hospital de la Santa Creu i Sant Pau de Barcelona and CIBERER, Madrid, Spain.
6 Developmental Dynamics, Myocardial Function, National Heart and Lung Institute, Imperial College London, London, United Kingdom.
7 Heart Science Centre, National Heart and Lung Institute, Imperial College London, London, United Kingdom.
8 Institute for Physiology and Pathophysiology, AG Vegetative Physiology, Philipps-University of Marburg, Marburg, Germany.
9 Institute for Molecular Plant Physiology and Biophysics, Julius-von-Sachs Platz 2, 97082, Würzburg, Germany.
10 Department of Clinical Genetics, Rigshospitalet, University of Copenhagen, Denmark.

PMID: 31610034 DOI: 10.1002/ana.25620

Abstract

Objective: The Popeye domain containing 3 (POPDC3) gene encodes a membrane protein involved in cyclic adenosine monophosphate (cAMP) signaling. Besides gastric Cancer, no disease association has been described. We describe a new muscular dystrophy associated with this gene.

Methods: We screened 1,500 patients with unclassified limb girdle weakness or hyperCKemia for pathogenic POPDC3 variants. Five patients carrying POPDC3 variants were examined by muscle magnetic resonance imaging (MRI), muscle biopsy, and cardiac examination. We performed functional analyses in a zebrafish popdc3 knockdown model and heterologous expression of the mutant proteins in Xenopus laevis oocytes to measure TREK-1 current.

Results: We identified homozygous POPDC3 missense variants (p.Leu155His, p.Leu217Phe, and p.Arg261Gln) in 5 patients from 3 ethnically distinct families. Variants affected highly conserved residues in the Popeye (p.Leu155 and p.Leu217) and carboxy-terminal (p.Arg261) domains. The variants were almost absent from control populations. Probands' muscle biopsies were dystrophic, and serum creatine kinase levels were 1,050 to 9,200U/l. Muscle weakness was proximal with adulthood onset in most patients and affected lower earlier than upper limbs. Muscle MRI revealed fat replacement of paraspinal and proximal leg muscles; cardiac investigations were unremarkable. Knockdown of popdc3 in zebrafish, using 2 different splice-site blocking morpholinos, resulted in larvae with tail curling and dystrophic muscle features. All 3 mutants cloned in Xenopus oocytes caused an aberrant modulation of the mechano-gated Potassium Channel, TREK-1.

Interpretation: Our findings point to an important role of POPDC3 for skeletal muscle function and suggest that pathogenic variants in POPDC3 are responsible for a novel type of autosomal recessive limb girdle muscular dystrophy. ANN NEUROL 2019;86:832-843.

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