The disease in which the sugar level of blood increases is known as diabetes mellitus. Diabetes mellitus is a chronic metabolic disorder that occurs when the body is unable to regulate blood sugar levels properly. This is typically caused by a lack of insulin production or the body`s inability to effectively use insulin. Option 2, diabetes insipidus, is a different condition that affects the ability to regulate water levels in the body. Option 3, diabetes imperfectus, and option 4, diabetes sugarensis, do not exist as recognized medical conditions. It is important to remember that diabetes mellitus can be further classified into type 1 diabetes and type 2 diabetes, but the common characteristic is elevated blood sugar levels.