By: Ben Eastman
In a new study from the U.K., cases of childhood type I diabetes were shown to cluster over time in geographic regions.
English children in the counties of North Yorkshire, West Yorkshire and Humberside were monitored from 1977 to 1990 for the distribution of cases of childhood type I diabetes. More pairs of diagnosed cases were found within one kilometer (km) and up to 900 days of each other than could be explained by chance. This clustering was still significant even after the researchers accounted for childhood population density and multiple cases within families.
The clustering was especially strong for younger age groups (0-5 and 5-9 years old). Previous research, from as far back as 1969, has shown that type I diabetes has other special characteristics within younger children. For example, seasonality appears to have little or no effect on the appearance of type I in younger children, unlike their older counterparts.
The study, published in the May 1997 Diabetes Care, found that the highest level of clustering was seen within one km and within a 360 day period. This is in agreement with a similar 1994 Swedish study that found cases of childhood type I clustered within 15 kms and seven months of each other. (Participants in the Swedish studies were from predominantly rural areas, so greater spatial clustering is expected.)
Clustering was especially strong during the period of 1982-85 and significantly different for the periods before and after. Other European studies like this one have shown similar time clustering: in Sweden from 1981-85 and Poland from 1982-85.
According to the U.K. study, changes in a population that is genetically susceptible to the disease can not account for clustering over such a short time period. Therefore, the researchers suspect that development of the disease may be related to an environmental factor that varies over time. An example of such a factor: an epidemic of infectious diseases that could be involved in the onset or promotion of Beta-cell destruction leading to type I diabetes.