The present invention discloses the identification of a fibrosis susceptibility gene locus, the IL22RA2 gene locus, which can be used for detecting predisposition to, diagnosis and prognosis of fibrosis as well as for the screening of therapeutically active drugs. The invention further provides a method for determining the likelyhood of a patient affected with a viral infection to respond to a treatment with an antiviral agent and/or an interferon, which method comprises determining alteration in IL22RA2 gene locus or in IL22RA2 expression or IL22RA2 protein activity in a biological sample of the patient.