Skeletal Muscle Involvement in Patients With Truncations of Titin and Familial Dilated Cardiomyopathy

Sofie Vinther Skriver, Bjørg Krett, Nanna Scharf Poulsen, Thomas Krag, Helle Rudkjær Walas, Alex Hørby Christensen, Henning Bundgaard, John Vissing, Christoffer Rasmus Vissing*

*Corresponding author for this work

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.

Original languageEnglish
JournalJACC. Heart failure
Volume12
Issue number4
Pages (from-to)740-753
Number of pages14
ISSN2213-1779
DOIs
Publication statusPublished - Apr 2024

Keywords

  • genotype
  • inherited cardiomyopathies
  • phenotype
  • truncating titin variants

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