HLA-related heterogeneity in seasonal patterns of diagnosis in Type 1 (insulin-dependent) diabetes

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Abstract
HLA type, time of year of diagnosis, and age at diagnosis were studied in 52 new cases of Type 1 diabetes in Seattle, Washington. Diagnosis was found to be seasonal in diabetic patients positive for DR3 (p< 0.005), with the expected marked reduction in new cases during the summer months. This seasonality was not age-related (p>0.13). Cases who were DR3-negative did not show significant seasonality of diagnosis (p>0.5). However, when age at diagnosis was adjusted for, a seasonal effect was found in the DR3-negative group (p<0.006), with older cases favouring a spring onset and younger cases favouring an autumn onset. Thus, DR3-positive cases showed a seasonal diagnosis pattern that did not depend on age, while DR3-negative cases showed an age-dependent seasonal pattern. These differences may reflect the predominance of different aetiological mechanisms in these two genetic groups.
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