(2) Considering the similar mechanism of Lp (a) and RLP-C in interfering with collateral growth, the weakened discriminative role of Lp (a) in T2DM patients could be partly explained by the increased association between estimated RLP-C and collateral development [OR (95%CI) 4.95(2.35–10.45) and 10.58 (4.77–23.45) in the T2 and T3 group, P < 0.001], indicating RLP-C could exert greater effect on the formation of coronary collateralization than Lp (a), especially in those T2DM patients. The gene discussed is LPA; the disease is type 2 diabetes mellitus.