In addition, transfection of pcDNA3.1‐SAMD1 into HUVECs in the control group significantly increased the expression of SAMD1 (Supporting Information: Figure 1A,B, p < .05), but did not change the levels of anti‐B2GPI and ACA, cell proliferation ability, and cell viability (Supporting Information: Figure 1C–F), which suggested that the effect of overexpressed SAMD1 seemed to be specific to APS. Here, SAMD1 is linked to autoimmune polyendocrinopathy.