title: Irisin and Myostatin Levels in Patients with Graves' Disease.
abstract: OBJECTIVE
  Skeletal muscle system, which is one of the primary targets for thyroid hormones, has an important role in energy metabolism. Some myokines such as irisin and myostatin have considerable effects on energy metabolism in addition to the musculoskeletal system. Our aim was to investigate circulating irisin and myostatin levels in patients with Graves' Disease (GD).
  
  
  METHODS
  This study included 41 patients with GD who were in overt hyperthyroid status and 44 healthy subjects.
  
  
  RESULTS
  Serum irisin levels were higher in patients with hyperthyroidism than in control group (p = 0.003). However, there was no statistical difference in myostatin levels between groups (p = 0.21). Irisin levels were positively correlated with free triiodothyronine (FT3), free thyroxine (FT4), thyrotropin receptor antibody (TRAb) (p = 0.03, p = 0.02, p = 0.02, respectively) and negatively correlated with thyroid-stimulating hormone (TSH) (p = 0.006) in both groups. In multiple regression analysis, the presence of GD was the only significant factor associated with serum irisin levels (β = 0.29, p = 0.01). Myostatin levels were positively correlated with age, body mass index (BMI), FT4, HOMA-IR (p = 0.001, p = 0.04, p = 0.003, p = 0.03, respectively) and negatively correlated with TSH (p = 0.01). Multiple regression analysis also revealed that age and FT4 were the significant factors associated with circulating myostatin levels (β = 0.27, p = 0.02; β = 0.22, p = 0.04, respectively).
  
  
  CONCLUSIONS
  Our results suggest that increased irisin levels might contribute to altered energy metabolism in hyperthyroidism. Further studies to determine whether myostatin is affected due to hyperthyroidism are needed.
authors.affiliation: Department of Endocrinology and Metabolism, Gazi University Faculty of Medicine, Ankara, Turkey. Electronic address: yalcin.muhittin@gmail.com.
authors.forename: Mehmet Muhittin
authors.initials: MM
authors.lastname: Yalcin
authors.affiliation: Department of Endocrinology and Metabolism, Gazi University Faculty of Medicine, Ankara, Turkey.
authors.forename: Mujde
authors.initials: M
authors.lastname: Akturk
authors.affiliation: Department of Internal Medicine, Gazi University Faculty of Medicine, Ankara, Turkey.
authors.forename: Yusuf
authors.initials: Y
authors.lastname: Tohma
authors.affiliation: Department of Endocrinology and Metabolism, Gazi University Faculty of Medicine, Ankara, Turkey.
authors.forename: Ethem Turgay
authors.initials: ET
authors.lastname: Cerit
authors.affiliation: Department of Endocrinology and Metabolism, Gazi University Faculty of Medicine, Ankara, Turkey.
authors.forename: Alev Eroglu
authors.initials: AE
authors.lastname: Altinova
authors.affiliation: Department of Endocrinology and Metabolism, Gazi University Faculty of Medicine, Ankara, Turkey.
authors.forename: Emre
authors.initials: E
authors.lastname: Arslan
authors.affiliation: Department of Endocrinology and Metabolism, Gazi University Faculty of Medicine, Ankara, Turkey.
authors.forename: Ilhan
authors.initials: I
authors.lastname: Yetkin
authors.affiliation: Department of Endocrinology and Metabolism, Gazi University Faculty of Medicine, Ankara, Turkey.
authors.forename: Fusun Balos
authors.initials: FB
authors.lastname: Toruner
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D004734:Energy Metabolism; D005260:Female; D005353:Fibronectins / Q000097:blood*; D006111:Graves Disease / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D055435:Myostatin / Q000097:blood*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: C577593:FNDC5 protein, human; D005353:Fibronectins; C525911:MSTN protein, human; D055435:Myostatin; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine
keywords: Graves' disease; Hyperthyroidism; Irisin; Myostatin