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Skriver SV, Krett B, Poulsen NS, Krag T, Walas HR, Christensen AH, Bundgaard H, Vissing J, Vissing CR. Skeletal Muscle Involvement in Patients With Truncations of Titin and Familial Dilated Cardiomyopathy. JACC Heart Fail 2024; 12:740-753. [PMID: 37999665 DOI: 10.1016/j.jchf.2023.10.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Revised: 09/29/2023] [Accepted: 10/03/2023] [Indexed: 11/25/2023]
Abstract
BACKGROUND Genetic variants in titin (TTN) are associated with dilated cardiomyopathy (DCM) and skeletal myopathy. However, the skeletal muscle phenotype in individuals carrying heterozygous truncating TTN variants (TTNtv), the leading cause of DCM, is understudied. OBJECTIVES This study aimed to assess the skeletal muscle phenotype associated with TTNtv. METHODS Participants with TTNtv were included in a cross-sectional study. Skeletal muscle fat fraction was evaluated by magnetic resonance imaging (compared with healthy controls and controls with non-TTNtv DCM). Muscle strength was evaluated by dynamometry and muscle biopsy specimens were analyzed. RESULTS Twenty-five TTNtv participants (11 women, mean age 51 ± 15 years, left ventricular ejection fraction 45% ± 10%) were included (19 had DCM). Compared to healthy controls (n = 25), fat fraction was higher in calf (12.5% vs 9.9%, P = 0.013), thigh (12.2% vs 9.3%, P = 0.004), and paraspinal muscles (18.8% vs 13.9%, P = 0.008) of TTNtv participants. Linear mixed effects modelling found higher fat fractions in TTNtv participants compared to healthy controls (2.5%; 95% CI: 1.4-3.7; P < 0.001) and controls with non-TTNtv genetic DCM (n = 7) (1.5%; 95% CI: 0.2-2.8; P = 0.025). Muscle strength was within 1 SD of normal values. Biopsy specimens from 21 participants found myopathic features in 13 (62%), including central nuclei. Electron microscopy showed well-ordered Z-lines and T-tubuli but uneven and discontinuous M-lines and excessive glycogen depositions flanked by autophagosomes, lysosomes, and abnormal mitochondria with mitophagy. CONCLUSIONS Mild skeletal muscle involvement was prevalent in patients with TTNtv. The phenotype was characterized by an increased muscle fat fraction and excessive accumulation of glycogen, possibly due to reduced autophagic flux. These findings indicate an impact of TTNtv beyond the heart.
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Affiliation(s)
- Sofie Vinther Skriver
- Copenhagen Neuromuscular Center, Department of Neurology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Bjørg Krett
- Copenhagen Neuromuscular Center, Department of Neurology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Nanna Scharf Poulsen
- Copenhagen Neuromuscular Center, Department of Neurology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Thomas Krag
- Copenhagen Neuromuscular Center, Department of Neurology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Helle Rudkjær Walas
- Copenhagen Neuromuscular Center, Department of Neurology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark
| | - Alex Hørby Christensen
- Department of Cardiology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark; Department of Cardiology, Copenhagen University Hospital, Herlev-Gentofte Hospital, Copenhagen, Denmark; Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - Henning Bundgaard
- Department of Cardiology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark; Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - John Vissing
- Copenhagen Neuromuscular Center, Department of Neurology, Copenhagen University Hospital, Rigshospitalet, Copenhagen, Denmark; Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
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