Seasonality of month of birth of patients with Graves' and Hashimoto's diseases differ from that in the general population

Objective: We aimed to test the viral hypothesis in the pathogenesis of autoimmune thyroid disease (AITD). Design: We determined the pattern of month of birth (MOB) distribution in patients with AITD and in the general population and searched for differences between them. Methods: A total of 1023 patients were included in this study: 359 patients had Graves' hyperthyroidism (GrH) and 664 had Hashimoto's hypothyroidism (HH). We divided the patients with HH into three subgroups according to their thyroid peroxidase (TPO) antibody titers at diagnosis: low levels (<500 IU/ml), high levels (500-1000 IU/ml). and extremely high levels (>1000 IU/ml). We used cosinor analysis to analyze the data. Results: Overall, patients with GrH and HH had a different pattern of MOB distribution when compared with the general population and between groups. Furthermore, among both patients with GrH and HH, both genders had a different pattern of MOB distribution when compared with the general population and this pattern was also different between genders. Finally, only women with extremely high titers of TPO antibodies at diagnosis and men with low or extremely high TPO antibody levels showed rhythmicity in MOB, with a pattern of MOB distribution different from that in controls. Conclusions: The different MOB seasonality in both GrH and HH points towards a similar maybe even common etiology with type 1 diabetes mellitus and multiple sclerosis, namely a seasonal viral infection as the initial trigger in the perinatal period, the clinical disease resulting from further specific damage over time.