Influence of Irisin on Muscle Quality in a Cohort of Charcot-Marie-Tooth Patients

Currently, there are no effective treatment approaches for CMT other than treating symptoms with medications such as nonsteroidal anti-inflammatory drugs that provide relief of lower back or leg pain. Except for the most severe cases in which orthopedic surgery is recommended to correct pes cavus and/or spine deformities, rehabilitative management of patients with CMT has shown that physical activity can provide a moderate increase in muscle strength and musculoskeletal function, improving activities of daily living. Benefits of exercise on the musculoskeletal system are widely recognized as primary non-pharmacologic intervention for several diseases. The positive outcome of physical activity is achieved not only by the mechanical load applied on the musculoskeletal system, but also via biochemical signals, the myokines, secreted during contraction that act locally or systemically on several body districts. Among these, Irisin is a hormone-peptide synthesized from skeletal muscle performing key actions on the whole-body metabolism. In humans, the investigators have documented with several studies an existing positive association between circulating levels of Irisin and bone mineral density. Very recently, in muscle biopsies of older adult subjects, the investigators also observed that the expression of the Irisin precursor, the fibronectin type III domain-containing protein 5 (FNDC5), was positively associated with Irisin serum levels and osteocalcin mRNA expression in bone biopsies, indicating a strong correlation between healthy muscle and bone tissues. In humans, low levels of circulating Irisin have been found to be predictive of muscle weakness and atrophy, and Irisin has been identified as a sensitive molecular biomarker for sarcopenia in postmenopausal women. In addition, women older than 65 years undergoing a 12-week exercise program showed an increase in circulating Irisin and an improvement in isokinetic leg strength and grip strength compared with control women. Moreover, there was a positive correlation between Irisin levels with grip strength and leg strength in the exercise group, suggesting a causal relationship between improved muscle strength and increased Irisin concentration. Although numerous reports recommend increasing muscle strength in CMT patients to prevent progressive distal weakness and muscle atrophy, few studies have investigated the possible key determinants of muscle quality in these patients. Therefore, the aim of this study was to evaluate circulating Irisin levels in a population of 20 CMT patients as well the association of Irisin with biochemical parameters and muscle quality. In addition, the investigators compared these data with unpublished data previously obtained in healthy subjects.