Abstract
Viral/bacterial infection is proposed as a trigger for the autoimmune thyroid diseases (AITD): Graves' disease (GD) and Hashimoto's thyroiditis (HT). Previous studies in European Caucasian AITD subjects found higher birth rates in the autumn/winter, suggesting those born in the autumn/winter experience increased viral/bacterial exposure after birth, impacting upon immune system development and predisposing to AITD later in life. Month of birth effects were investigated in three independent European Caucasian AITD datasets. Variation in GD and HT onset was compared across months and seasons, with fluctuations across all 12 months analyzed using a Walter-Elwood test. The study was conducted at a research laboratory. National UK Caucasian AITD Case Control Collection (2746 GD and 502 HT compared with 1 423 716 UK births), National UK Caucasian GD Family Collection (239 GD and 227 unaffected siblings), and OXAGEN AITD Caucasian Family Collection (885 GD, 717 HT, and 794 unaffected siblings of European Caucasian decent). Case-control and family-based association studies were measured. No consistent month of birth effects were detected in GD females or males across all three collections. In HT females from the OXAGEN AITD Caucasian Family Collection, slightly higher birth rates were detected in autumn (Walter's test statistic = 7.47, P = .024) however, this was not seen in the HT females from the case-control cohort. Our results suggest in UK/Northern European Caucasian GD subjects, month of birth does not impact on AITD development. Although some month of birth effects for HT females in one collection cannot be excluded, only further work in larger European Caucasian AITD collections can confirm these effects.
Highlights
Design: Variation in Graves’ disease (GD) and Hashimoto’s thyroiditis (HT) onset was compared across months and seasons, with fluctuations across all 12 months analyzed using a Walter-Elwood test
No consistent month of birth effects were detected in GD females or males across all three collections
In HT females from the OXAGEN autoimmune thyroid diseases (AITD) Caucasian Family Collection, slightly higher birth rates were detected in autumn (Walter’s test statistic ϭ 7.47, P ϭ .024) this was not seen in the HT females from the case-control cohort
Summary
Caucasian AITD Case Control Collection (2281 GD females, 465 GD males, 433 HT females, and 69 HT males) compared against 1 423 716 UK births from 1956 through 1957 [12]. The National UK Caucasian GD Family Collection (206 GD females, 33 GD males, 132 unaffected female siblings, and 95 unaffected male siblings) were recruited from the same centers as the National UK Caucasian AITD Case Control Collection (see Supplemental Methods). The OXAGEN AITD Caucasian Family Collection (762 GD females, 123 GD males, 632 HT females, 85 HT males, 460 unaffected female siblings, and 334 unaffected male siblings) were collected from centers in the United Kingdom (Birmingham, Cambridge, Glasgow, Oxford, and Sheffield), Denmark, and The Netherlands [12, 13] (see Supplemental Methods for further information on recruitment criteria and geographical location of centers contributing to these collections). Because AITD exhibits a strong female preponderance, all month-of birth-data were split by gender
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