Facioscapulohumeral muscular dystrophy (FSHD), an autosomal dominant disorder, is one of the most common muscular dystrophy in adults in Europe [[1], [2], [3]]. It is initially characterized by weakness and atrophy of face and scapular muscles [4]. The muscle weakness pattern is often asymmetrical [4] and its progression rate and extent may vary considerably, with sudden periods of unexplained rapid disease progression [5,6]. FSHD type I (FSHD1), the major FSHD form, is genetically linked to deletions in chromosome 4q35 within the D4Z4 repeat array [7]. This is associated with DNA hypomethylation [[8], [9], [10]], resulting in the toxic misexpression of the double-homeodomain transcription factor DUX4 [11,12]. In myoblasts, this transcription factor induces various signaling pathways that lead to muscle differentiation defects, muscle atrophy and oxidative stress [11,[13], [14], [15]], which are FSHD key features [16]. Besides DUX4, other genes in the 4q35 region [e.g. double homeobox 4 centromeric (DUX4c), adenine nucleotide translocator 1 (ANT1), FSHD region gene 1 and 2 (FRG1, FRG2)] might be derepressed and act as modifiers [[17], [18], [19], [20], [21]], contributing to FSHD pathogenesis, either independently or synergistically. Despite major progress in understanding FSHD genetic basis, the specific pathogenic mechanisms remain unclear. To date, no curative treatment is available. Increasing evidence suggests that free radical-mediated oxidative stress plays a major role in FSHD pathogenesis [20,[22], [23], [24], [25], [26], [27]]. We recently reported that reduced physical performance in patients with FSHD is associated with systemic redox unbalance and oxidative stress [23]. Specifically, we demonstrated that patients with FSHD showed higher levels of oxidative damage (lipid peroxide and oxidized DNA levels) and significantly lower GSH/GSSG ratio (due to GSSG accumulation). Although no significant difference was found between FSHD and control blood samples concerning superoxide dismutase (CuZn-SOD) and glutathione peroxidase (GSH-Px) levels, most of patients had significantly lower levels of zinc (a SOD cofactor), selenium (a GSH-Px cofactor involved in the elimination of lipid peroxides), and vitamin C compared to healthy controls. The importance of maintaining adequate levels of zinc and selenium is emphasized by studies indicating that low antioxidant status may be associated with increased risk of developing various diseases [[28], [29], [30]]. Selenium was given as selenomethionine because its bioavailability is nearly twice that of selenium as selenite [31]. Zinc gluconate was used because it is absorbed more efficiently [32]. Vitamin C, the major water soluble antioxidant, and vitamin E (a lipid-soluble vitamin found in cell membranes and circulating lipoproteins) were selected due to their protective effects against lipid peroxidation in humans [[33], [34], [35]]. Alpha tocopherol is the vitamin E form that is preferentially absorbed and accumulated in humans [36].

As oxidative stress can affect skeletal muscle contractibility and function, we hypothesized that oxidative stress is a potential mechanism of peripheral muscle dysfunction and impaired exercise performance in FSHD. To test this hypothesis, we performed a randomized placebo-controlled trial to assess the benefits of antioxidant supplementation, based on the synergic effect of vitamin C, vitamin E, zinc and selenium, on muscle function and oxidative stress biomarkers in 53 patients with FSHD (NCT01596803). In this randomized placebo-controlled clinical trial, at the end of the 17 weeks of treatment, we observed a benefit on the strength of both quadriceps (primary endpoint), the antioxidant defenses and oxidative stress (secondary endpoints), supporting a role for FSHD-induced oxidative stress in quadriceps strength reduction [24]. From this study, although markers related to oxidative stress (VitC, Zinc, etc.) are within normal range, our data suggest that optimal antioxidant protection requires synchronously optimized vitamin C and E dosage. Moreover, our data suggest also that the Cu/Zn ratio and copper level are more important than the level of zinc alone.

In the present study, we evaluated muscle and fat volumes in quadriceps muscles (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis) by Magnetic Resonance Imaging (MRI) and investigated their relationships with muscle strength and oxidative stress markers in 32 patients with FSHD and 7 healthy controls. We also investigated the cytoskeletal ultrastructural organization of vastus lateralis by transmission electron microscopy (TEM). Lastly, in 20 patients with FSHD, we investigated the effect of 17-week antioxidant supplementation or placebo on quadriceps muscle parameters, muscle strength, oxidative stress markers and quality of life.