LAUSR

Dear Editor, We would like to thank Laurent et al. for their interest and comments about our article published in Gerontology [1, 2]. We think that their statements show the way to future investigations on the role of myostatin as a biomarker of the conditions of frailty/sarcopenia. We would also like to thank the Editor for giving us the opportunity to add some comments to complete the information provided in the Letter to the Editor entitled “Myostatin: a powerful biomarker for sarcopenia and frailty?”. First, we agree with Laurent et al. that additional research is needed to analyze the relation between myostatin and frailty or sarcopenia separately. In fact, most of the published studies analyzed the association of blood myostatin with different parameters such as age or physical interventions related to both conditions [3, 4], but few of them assessed frailty by using validated scales [2], or sarcopenia by accurate methods such as dual-energy X-ray absorptiometry [5, 6]. These methodologies should be used in further studies aimed at analyzing the role of myostatin as a biomarker of frailty or sarcopenia. Secondly, the relationship between levels of circulating myostatin and frailty/sarcopenia-related parameters seems to be highly dependent on age, sex, and comorbidities [7–9] and contradictory associations have been reported, depending on the population under study [5]. The lack of specificity of some enzyme-linked immunosorbent assay methods might have increased this controversy [9]. These issues should be clarified before proposing myostatin as a biomarker of both conditions; we recommend carrying out studies, using accurate methods to measure myostatin such as mass spectrometry and with large, wide samples in which the population could be segmented by sex, age, physical fitness or other parameters. Finally, recent studies have described that blood myostatin concentration increased in the 24 h following an acute boot of physical exercise [10]. Thus, in interventional studies, depending on the time elapsed between the physical exercise session and blood extraction, contradictory results could be obtained. Therefore, before using myostatin as a biomarker for diagnosis or prognosis of frailty/sarcopenia, it seems necessary to carry out further investigation to define the most appropriate time lapse between physical exercise and blood extraction. Additionally, specific recommendations on the level of physical activity on the days prior to testing could be necessary before blood analysis to measure myostatin is carried out. In conclusion, we agree with Laurent et al., who stated that blood biomarkers such as myostatin could be highly useful to identify those people at risk for developing frailty or sarcopenia. This knowledge could contribute to the early diagnoses and prognosis of both conditions. However, further studies are needed to clarify the role of myostatin in different populations.