Interplay between heredity and environment in the recent explosion of type 1 childhood diabetes mellitus.

The fast increase in the incidence of childhood type 1 diabetes mellitus (T1DM) that cannot be explained by changes in the genetic susceptibility, led us to look for environmental causes. To test the hypothesis that the initiation of the autoimmune process of childhood T1DM in genetically susceptible subjects begins in the perinatal period by a viral infection, we studied the seasonal variations in the month of birth of several cohorts of patients compared to the general population. Population groups with high or low T1DM incidence were analyzed separately by t-test and the Cosinor methods. In areas with populations with a high incidence (Israeli Jews, Sicily, Sardinia, Slovenia, Germany) we found that the children (in Sicily also young adults) who subsequently developed T1DM, have a higher incidence of births in the summer months than in other seasons of the year, a mirror image of the seasonality of the clinical onset of disease. This pattern differed significantly from the seasonality of the total live births in the same populations. In populations with a low T1DM incidence, (China, Japan and Cuba) no seasonality of month of birth was found. Similar findings have been reported, from five counties in the U.K. and the Netherlands. It is hypothesized that mothers who become pregnant during the period of yearly viral epidemics transmit to the fetus, either a virus or antiviral antibodies, which determine whether an autoimmune process against the pancreatic beta is initiated or whether the fetus is protected against that process. Copyright 2002 Wiley-Liss, Inc.