Increasing incidence of Type 1 diabetes – role for genes?
1 Department of Mathematics and Statistics, Rolf Nevanlinna Institute, P.O. Box 4 (Yliopistonkatu 5), FIN-00014 University of Helsinki, Finland
2 Department of Computer Science, Helsinki Institute of Information Technology, Basic Research Unit, P.O. Box 26 (Teollisuuskatu 23), FIN-00014 University of Helsinki, Finland
3 Department of Epidemiology and Health Promotion, National Public Health Institute, Diabetes and Genetic Epidemiology Unit, Mannerheimintie 166, FIN-00300 Helsinki, Finland
BMC Genetics 2004, 5:5 doi:10.1186/1471-2156-5-5Published: 2 April 2004
The incidence of Type 1 diabetes (T1DM) is increasing fast in many populations. The reasons for this are not known, although an increase in the penetrance of the diabetes-associated alleles, through changes in the environment, might be the most plausible mechanism. After the introduction of insulin treatment in 1930s, an increase in the pool of genetically susceptible individuals has been suggested to contribute to the increase in the incidence of Type 1 diabetes.
To explore this hypothesis, the authors formulate a simple population genetic model for the incidence change driven by non-Mendelian transmission of a single susceptibility factor, either allele(s) or haplotype(s). A Poisson mixture model is used to model the observed number of cases. Model parameters were estimated by maximizing the log-likelihood function. Based on the Finnish incidence data 1965–1996 the point estimate of the transmission probability was 0.998. Given our current knowledge of the penetrance of the most diabetic gene variants in the HLA region and their transmission probabilities, this value is exceedingly unrealistic.
As a consequence, non-Mendelian transmission of diabetic allele(s)/haplotype(s) if present, could explain only a small part of the increase in incidence in Finland. Hence, the importance of other, probably environmental factors modifying the disease incidence is emphasized.