SDHD and Down syndrome: To determine the interrelationships between key biomarkers and clinical phenotypes including syndromes and cardiac function-related indicators, Spearman correlation analysis was performed between DEGs, DEPs, DMs and NT-proBNP, LVEF, LVEDD, LVEDV, SV, 6WMD, MLHFQ, symptoms/signs and syndrome scores of the three syndrome types, respectively.The results showed that in QDBS, SDHD and COX5A were significantly correlated with 6MWD, VWF with MLHFQ, Succinic Acid with NT-proBNP, Valeric acid with LVEDV, and multiple biomarkers showing significant correlations with QDBS syndrome (Figure 4D).