Here, based on LightGBM, we utilized XIST (X Inactive Specific Transcript, 300936) as an effective gene signature to identify both hypertrophic cardioMyopathy (up-regulation) and HF-hypoplastic left heart syndrome (down-regulation), specifically in fibroblasts, which have already been supported by previous publications [69,70]. The gene discussed is XIST; the disease is hydrops fetalis.