INS and diabetes mellitus: Moreover, although the distinction between the two main types of diabetes, type 1 (T1D) and type 2 (T2D), has historically been based on age at onset, degree of loss of β-cell function, degree of insulin resistance, presence of diabetes-associated autoantibodies, and need for insulin treatment, none of these characteristics clearly distinguish one type of diabetes from another, nor do they account for the full spectrum of diabetes phenotypes [4].