Baseline: EB-HF showed hypermethylated DNA (60%) compared to ED-LF. Post-exercise: EB-HF: significant hypomethylation in regulatory regions (CpG islands) and ↑ expression of HDAC2, MECR, IGF2, and c13orf16; ED-LF: ↑ expression of HDAC11; EB-HF: epigenetic and transcriptional changes that support exercise recovery and metabolism. The gene discussed is HDAC2; the disease is hydrops fetalis.