Differences between males and females in the seasonality of birth and month of clinical onset of disease in children with type 1 diabetes mellitus in Ireland.

The aim was to study the monthly rhythm of birth and clinical onset in 303 children with type 1 diabetes mellitus (DM1) aged 0-15 years (156 males, 147 females) born between 1980 and 1996 in Ireland and compare to 951,717 infants born in the general population during the same period. Analysis was performed using the cosine fit for rhythm and t-test between the seasons of the year. Whereas the males showed a rhythmic pattern of month of birth, peaking in the summer (p < 0.05), similar to that in the general population, the females showed no seasonal differences in either month of birth or month of onset. A mirror image pattern, nadir in spring and summer (p < 0.01), was observed in month of clinical onset, also only in males. If we assume a viral infectious etiology of DMI, females seem to be less susceptible than males to the environmental infectious influences.