1. Diabetes Centre, Isala Clinics, Zwolle, the Netherlands;
2. Langerhans Medical Research Group, Zwolle, the Netherlands;
3. General Practice, Sleeuwijk, the Netherlands;
4. Department of General Practice, University Medical Center Groningen, Groningen, the Netherlands;
5. University of Groningen, Groningen, the Netherlands;
6. Department of Internal Medicine, University Medical Center Groningen, Groningen, the Netherlands.