The present invention relates to a method for identifying a compound capable of modulating the action of the DLG5 protein which method comprises subjecting one or more test compounds to a screen comprising a polypeptide containing the amino acid sequence shown in SEQ ID NO: 2, or a homologue thereof or a fragment of either. Such compounds may be useful in the treatment of inflammatory bowel disease. The present invention also relates to a method for diagnosing inflammatory bowel disease by detecting variant DLG5.