The present application identifies the involvement of the HIFβ-homologous Arntl2 gene in the control of type 1 (insulin-dependent) diabetes. Accordingly, the present invention provides a method of determining the susceptibility of a subject to developing insulin-dependent diabetes based on the expressing level of the Arntl2 gene. The present invention also provides a method for identifying compounds effective for treating or preventing insulin-dependent diabetes in a subject in need thereof and a method of treating or preventing insulin-dependent diabetes by administering an effective amount of compound identified by the identification method. The present invention also provides a method of enhancing protection against insulitis progression or autoimmune diabetes development in a subject in need thereof comprising, enhancing expression of the Arntl2 gene or modulating the expression of target genes thereof.