MSTN and sarcopenia: In the group of HD and PD patients, those with sarcopenia were characterized by lower myostatin concentrations compared to non-sarcopenic patients (HD group: 2792.8 ± 1276 pg/mL vs. 4428.7 ± 2345 pg/mL; p < 0.001; PD group: 4358.7 ± 2388.8 pg/mL vs. 7436.5 ± 2475.2 pg/mL; p = 0.008).