LAUSR

Duchenne muscular dystrophy (DMD)-related osteoporosis is of increasing interest due to the extended life expectancy of DMD patients. Although considerable knowledge is available about the pathogenesis of bone fragility in DMD, new clinical and biochemical facets could enhance the prediction of fracture risk and consequently contribute to the optimal management of these patients. Hence, the comments to our article proposed by Finsterer and Strobl [1] encourage further human researches focused on fracture risk in DMD and at the same time highlight the complexity of DMD and the usefulness of multidisciplinary approach. As they point out, skeletal deformities in DMD patients could theoretically enhance the risk of fall and fracture. However, because of the small sample size, we did not categorize patients according to deformities or to a genetic basis. Skeletal deformities were observed in all the patients as part of the overall life course and in an age-related manner. Furthermore, we did not analyze the association between the degree of deformity and bone mineral density: patients with deformities such that they could not undergo bone scan through DXA densitometer (e.g., severe kyphosis or scoliosis) were not included in the study. As well, we excluded patients with NYHA class IV heart failure or a ventricular ejection fraction ≤ 30%, or those who needed the necessity of non-invasive ventilation for 24 h/day or with the presence of a tracheostomy, such as patients with severe form of heart or respiratory insufficiency, respectively. In this regard, none of the patients showed acidosis due to ventilation deficit at the time of enrollment. We noted forced vital capacity (FVC) correlated positively with BMD Z scores in DMD, irrespective of genetic background of DMD, and in accordance with several data in the literature on chronic obstructive pulmonary disease, indicating that patients with worse lung function parameters are more likely to have low BMD or osteoporosis; additionally, these patients show lower fat-free mass index and the presence of sarcopenia consistent with impaired muscle mass too [2]. We also hypothesize that systemic hypoxia could contribute to cell damage and systemic inflammation potentially involving bone tissue as well. Moreover, we might speculate DMD patients with lower FVC are more likely not ambulant and therefore have a lower BMD. In our study sample, median value of dietary calcium intake was substantially below the threshold of the recommended dose proposed by the Institute of Medicine. However, vitamin D was routinely administered and PTH concentration was within the normal range, suggesting a normal phospho-calcium metabolism. No correlations were found between serum calcium and any of the valued parameters including BMD Z score. This study did not investigate adipokines, but in light of the pathophysiology of DMD-related osteoporosis, the contribution of some mechano-responsive cytokines such as lipocalin-2 on BMD and fracture risk could be explored in further research [3].