One form of maturity-onset diabetes of the young, Type 3 (MODY3), results from mutations in the gene coding for hepatocyte nuclear factor-1alpha (HNF-1alpha), a transcription factor first described in the liver. MODY3 is characterized by a defective glucose-stimulated insulin secretion. Earlier observations of glycosuria with normal blood glucose levels in some MODY families suggest an additional renal manifestation of the respective genetic defect. We measured the renal threshold for glucose in five diabetic carriers of a missense mutation (Arg 272 His) in HNF-1alpha and, for comparison, in eight Type 1 diabetic patients, applying a non-invasive protocol of frequent parallel blood and urine sampling during a slow shift in blood glucose levels. We found that the mean renal threshold for glucose was lowered in the HNF-1alpha diabetic patients compared to those with Type 1 diabetes (6.5 +/- 0.9 mmol l(-1) vs 10.7 +/- 0.5 mmol l(-1); p < 0.01). This lowered glucose threshold might be an indication of an extra-pancreatic effect of HNF-1alpha gene mutations in humans. Defects in HNF-1alpha may lead to an altered tubular glucose reabsorption, possibly due to decreased expression of the renal glucose transporter proteins involved in reabsorption of glucose from the urine.

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We have recently shown that mutations in the gene encoding the transcription factor hepatocyte nuclear factor (HNF)-1alpha are the cause of one form of maturity-onset diabetes of the young (MODY3). Here, we report the exon-intron organization and partial sequence of the human HNF-1alpha gene. In addition, we have screened the ten exons and flanking introns of this gene for mutations in a group of 25 unrelated white subjects from Germany who presented with NIDDM before 35 years of age and had a first-degree relative with NIDDM. Mutations were identified in nine of these individuals, suggesting that mutations in the HNF-1alpha gene are a common cause of diabetes in German subjects with early-onset NIDDM and a family history of diabetes. Thus, screening for mutations in this gene may be indicated in subjects with early-onset NIDDM. Interestingly, three of the nine mutations occurred at the same site in exon 4 with insertion of a C in a polyC tract, centered around codon 290 (designated Pro291fsinsC), thereby resulting in a frameshift during translation and premature termination. Analyses of linked DNA polymorphisms in the HNF-1alpha gene indicated that the Pro291fsinsC mutation was present on a different haplotype in each subject, implying that the polyC tract represents a mutational hot spot. We have also identified the mutation in the HNF-1alpha gene in the Jutland pedigree, one of the original MODY pedigrees reported in the literature, as being a T-->G substitution in codon 241, resulting in the replacement of a conserved Cys by Gly (C241G). The information on the sequence of the HNF-1alpha gene and its promoter region will facilitate the search for mutations in other subjects and studies of the role of the gene in determining normal beta-cell functions.

In type 1 diabetes, GAD65 antibodies are initially generated against the middle and C-terminal regions of GAD65. In genetically predisposed subjects the autoimmune response may then undergo intramolecular epitope spreading towards epitopes on the N-terminus and further epitopes located in the middle. These findings clearly demonstrate that the GAD65 autoantibody response in the preclinical stage of type 1 diabetes is dynamic and related to the HLA genotypes that confer risk of diabetes. GAD65-specific Fab should prove useful in predicting progression from islet autoimmunity to clinical onset of type 1 diabetes.

Aims/hypothesis: Insulin autoantibodies (IAA) precede and predict the onset of type 1 diabetes, but not all children with IAA develop the disease. In affected families, IAA affinity can identify IAA-positive children who are more likely to progress to diabetes. The purpose of this study was to determine whether affinity is a useful marker to stratify type 1 diabetes risk in IAA-positive children from the general population. Methods: IAA affinity was determined by competitive binding to 125 Iinsulin with increasing concentrations of cold insulin and with cold proinsulin in sera from 46 IAA-positive children identified in the Karlsburg Type 1 Diabetes Risk Study of a Normal Schoolchild Population in north-eastern Germany. Results: IAA affinity ranged between 5×10 6 and 1.2×10 11 l/mol. IAA affinity was higher in 24 children who developed multiple islet autoantibodies or diabetes (median 3.5×10 9 l/mol; interquartile range [IQR] 2.1×10 9 to 2.1×10 10 l/mol) than in 22 children who did not develop multiple islet autoantibodies or diabetes (median 1.3×10 8 l/mol; IQR 3.8×10 7 to 7.2×10 8 l/mol; p<0.0001). Using a threshold of ≥10 9 l/mol, 22 of the 24 children who developed multiple islet autoantibodies or diabetes were correctly identified by high-affinity IAA and 18 of 22 who did not develop multiple islet autoantibodies or diabetes were correctly identified by low-affinity IAA. IAA affinity was significantly higher in samples with proinsulin reactive IAA (p<0.0001). Conclusions/interpretation: IAA affinity measurement provides robust identification of IAA associated with high diabetes risk.