The present disclosure relates generally to treatment and diagnosis of diseases, disorders or conditions characterized by vascular leakage. More particularly, the present disclosure relates to methods for treating a vascular leakage-associated disease or disorder in a subject; for reducing vascular leakage in a subject; for reducing reactive oxygen species production in a subject; for inducing apoptosis of neutrophils in a subject; and for increasing survival of a subject having a vascular leakage-associated disease or disorder. The methods comprise administering a G9a and/or G9a-like protein (GLP) methyltransferase inhibitor to the subject. The present disclosure further relates to methods for developing a treatment plan for a subject with a vascular leakage-associated disease, disorder or condition, and for identifying a subject as a candidate for treatment of a vascular leakage-associated disease or disorder. The present disclosure relates to use of G9a and/or G9a-like protein (GLP) methyltransferase inhibitor in the treatment of vascular leakage-associated disease, disorder or condition.