A long lupus-sensitive aPTT was significantly correlated with a higher level of IgG-isotype antibodies against domain I of β2-GPI (rho = 0.40, p < 0.0001) and a lower prothrombin time (given as percent of normal, rho = –0.27, p = 0.0007). The gene discussed is F2; the disease is systemic lupus erythematosus.