The present invention provides a method for assessing the presence and risk of developing type 2 diabetes, cancer of all sites, or cardiovascular disease in a subject by detecting sequence variation in one or more genes such as carboxypeptidase E (CPE) and insulin degradation enzyme (IDE). A kit, array, and device useful for such a method are also provided. In addition, the present invention provides a method for treating type 2 diabetes, cancer of all sites, or cardiovascular disease in patients who have been tested and shown to have the pertinent genetic variations.