OBJECTIVE: To investigate whether there are forms of early-onset autosomal-dominant type 2 diabetes that are distinct from typical maturity-onset diabetes of the young (MODY) and to characterize their phenotypic characteristics. RESEARCH DESIGN AND METHODS: The study included 220 affected subjects from 29 families in which early-onset type 2 diabetes occurred in multiple generations and was not linked to known MODY genes (MODY gene-negative families). All individuals underwent an oral glucose tolerance test and other clinical measurements aimed at investigating the underlying metabolic defect and the presence of diabetic complications. For comparison, 79 affected carriers of MODY3 (hepatocyte nuclear factor [HNF]-1 alpha) mutations were similarly examined. RESULTS: Subjects from MODY gene-negative pedigrees were diagnosed with diabetes at an older age (36 +/- 17 vs. 21 +/- 10 years, P = 0.0001) and were more frequently obese (52 vs. 18%, P = 0.0001) than MODY3 individuals. MODY gene-negative patients who were insulin treated required more exogenous insulin than did MODY3 subjects (0.7 +/- 0.4 vs. 0.45 +/- 0.2 U.kg-1.day-1, P = 0.04), despite similar C-peptide levels. Among subjects not treated with insulin, MODY gene-negative subjects had significantly higher serum insulin levels, both fasting (16.5 +/- 15 vs. 6.5 +/- 5 microU/ml, P = 0.027) and 2 h after a glucose load (53 +/- 44 vs. 11 +/- 10, P = 0.002). They also had higher serum triglycerides (P = 0.02), higher cholesterol levels (P = 0.02), more hypertension (P = 0.0001), and more nephropathy (P = 0.001). Differences persisted when families were matched for age at diagnosis. CONCLUSIONS: Our findings indicate the existence of forms of early-onset autosomal-dominant type 2 diabetes that are distinct from MODY and are frequently characterized by insulin resistance, similar to later-onset type 2 diabetes. Because of the Mendelian pattern of inheritance, the goal of identifying the genes involved in these forms of diabetes appears to be particularly feasible.

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