Mosaic pancreas or type 3 diabetes: how do we define it?

To document the existence and clinical characteristics of probands from families with multigenerational inheritance of early onset type 2 diabetes mellitus in Jamaica. Three probands from large families with multigenerational inheritance of early onset type 2 diabetes mellitus in at least three generations were detected at the University Hospital of the West Indies, Jamaica during a screening process for patients with MODY. Clinical, metabolic and genetic assessments were undertaken to ascertain the profile of the diabetes present in the three families. The three probands: patients 1, 2 and 3 were from families with history of ≥ 3 generations of early onset type 2 diabetes mellitus. All were diagnosed before age 25 years. The probands had varying metabolic profiles at the onset of diabetes ranging from decreased insulinaemia to hyperinsulinaemia (4.7 mU/L, 15.6 mU/L, 38.6 mU/L). The HbA_1c ranged from 12.1 to 18.4%. Two of the probands were of normal weight, the other obese (30.7 kg/m²). All probands had insulin resistance. Sequence variants in MODY 1–6 genes were absent in the probands and family members. Islet cell antibodies (ICA) were absent in two patients and the families of all three patients. However the third patient had a positive titre for the ICA antibodies. The clinical patterns of the diabetes seen in the three Jamaican families are difficult to include in a single type of diabetes mellitus. It is proposed to name this diabetes process Mosaic Pancreas or type 3 diabetes.