Impact of month of birth on the development of autoimmune thyroid disease in the United Kingdom and Europe

Seasonality of month of birth in patients with autoimmune endocrine diseases: A systematic review

BACKGROUND

Exposure to seasonal environmental factors during gestation or early in the postnatal period could influence the development of autoimmunity, determining a seasonality in the month of birth (MOB). There are studies evaluating this potential seasonality in patients with type 1 diabetes (T1D), autoimmune thyroid diseases (AITD), and Addison's disease (ADD), but results have been controversial.

METHODS

Systematic review according to PRISMA guidelines, using PubMed, Web of Science and WorldCat databases (2005-2020) of studies that explored the association between the seasonality of the MOB and T1D, AITD and ADD. Information on sex and age, location, methodology and internal quality, seasonal patterns, hypotheses and other factors proposed to explain seasonality were extracted. Differences in season and month of birth were further discussed.

RESULTS

The initial search retrieved 300 articles, and after further screening, 11 articles fulfilled inclusion criteria and were finally selected and reviewed. 73% found a seasonal pattern and 64% showed birth peaks in spring and/or summer. Hashimoto's thyroiditis and women exhibited a higher seasonality. Ultraviolet radiation, Vitamin D levels and viral infections were identified as influencing factors.

CONCLUSIONS

The effect of certain seasonal factors during foetal development, reflected by the seasonal differences in the MOB, could contribute to the development of endocrine autoimmune diseases in predisposed patients. Further research is needed to elucidate the mechanisms underlying the observed seasonality.

Vitamin D and Autoimmune Thyroid Disease-Cause, Consequence, or a Vicious Cycle?

Vitamin D is a steroid hormone traditionally connected to phosphocalcium metabolism. The discovery of pleiotropic expression of its receptor and of the enzymes involved in its metabolism has led to the exploration of the other roles of this vitamin. The influence of vitamin D on autoimmune disease-namely, on autoimmune thyroid disease-has been widely studied. Most of the existing data support a relationship between vitamin D deficiency and a greater tendency for development and/or higher titers of antibodies linked to Hashimoto's thyroiditis, Graves' disease, and/or postpartum thyroiditis. However, there have also been some reports contradicting such relationships, thus making it difficult to establish a unanimous conclusion. Even if the existence of an association between vitamin D and autoimmune thyroid disease is assumed, it is still unclear whether it reflects a pathological mechanism, a causal relationship, or a consequence of the autoimmune process. The relationship between vitamin D's polymorphisms and this group of diseases has also been the subject of study, often with divergent results. This text presents a review of the recent literature on the relationship between vitamin D and autoimmune thyroid disease, providing an analysis of the likely involved mechanisms. Our thesis is that, due to its immunoregulatory role, vitamin D plays a minor role in conjunction with myriad other factors. In some cases, a vicious cycle is generated, thus contributing to the deficiency and aggravating the autoimmune process.

Seasonality of month of birth in children and adolescents with autoimmune thyroiditis: a continuing conundrum

Background The aim of this study was to analyze the seasonal birth month pattern in young patients with autoimmune thyroiditis and compare it with youth controls. Methods Medical records of a total of 298 children and adolescents of Greek origin, with a diagnosis of Hashimoto thyroiditis (HT) before the age of 21 years that were born from 1987 to 2010 were retrospectively reviewed. In addition, 298 consecutive subjects that were born from 1988 to 2012 and evaluated in a tertiary unit for any reason, served as controls, provided that they had no personal or family history of thyroid or any other autoimmune disease. Results Significant differences were found between children and adolescents with HT and healthy controls in the yearly pattern of month of birth distribution (p=0.029). During month-by-month analysis, it was shown that the highest and lowest predispositions to HT were among those born in spring (March) (odds ratio [OR] 2.34, p=0.005), and autumn (November) (OR 0.49, p=0.035), respectively. A binary logistic regression model also revealed that season of birth and sex were the only factors that remained related to HT disease, even after adjustment for confounding factors such as year of birth and age (p<0.001, Nagelkerke r-square 0.151). Conclusions This study suggests that the effect of certain seasonal factors during fetal development, reflected by the seasonal differences in birth pattern, in children and adolescents with autoimmune thyroiditis could contribute to long-term programming of an autoimmune response against the thyroid gland. Further studies are needed to demonstrate a clear cause and effect relationship between month of birth and HT.

No link between season of birth and subsequent development of Graves' disease or toxic nodular goitre: a nationwide Danish register-based study

BACKGROUND

Season of birth, an exogenous indicator of early life environment, has been linked with a higher risk of adverse health outcomes such as autoimmune thyroiditis, multiple sclerosis and schizophrenia later in life. Whether the development and cause of hyperthyroidism is influenced by season of birth is unclarified. We aimed, at a nationwide level, to investigate whether season of birth influences the risk of hyperthyroidism due to Graves' disease (GD) and/or toxic nodular goitre (TNG).

METHOD

Register-based nationwide cohort study. By record-linkage between Danish health registers, 36,087 and 20,537 patients with GD and TNG, respectively, were identified. Each case was matched with four controls without thyroid disease, according to age and sex. Differences in month-of-birth across the year were evaluated by the Walter-Elwood test. Hazard ratios, for the risk of GD and TNG in individuals born in a certain month or season of the year, were calculated using Cox regression models.

RESULTS

Neither for GD nor for TNG could we demonstrate a significant difference in birth rate across months or seasons of the year (Walter-Elwood's test; X2 = 5.92 and X2 = 1.27, p = 0.052 and p=0.53, respectively).

CONCLUSION

Irrespective of its cause, our findings do not support the hypothesis that season of birth is significantly related to the development of hyperthyroidism.

Month of birth is associated with the subsequent diagnosis of autoimmune hypothyroidism. A nationwide Danish register-based study

BACKGROUND

The triggering of thyroid autoimmunity in the genetically susceptible remains a conundrum. Environmental exposures during gestation and/or early postnatally have proponents, as suggested in diabetes mellitus, with a higher incidence of births during spring and summer. Whether the development of autoimmune hypothyroidism (AIT) is influenced by month or season of birth is less clear.

METHOD

Nationwide cohort study of 111 565 individuals diagnosed with AIT and four euthyroid controls per case, matched according to age and sex, were identified from Danish health registers. Differences in month of birth across the year were evaluated by the Walter-Elwood test. The risk of patients with AIT being born in a certain month or season of the year was calculated using a Cox regression model.

RESULTS

There was a significant difference in birth month between cases and controls, P<.001. Individuals with AIT had a significantly increased risk of being born in June (Hazard ratio 1.04; 95% Confidence interval (CI): 1.02-1.08) and in the summer (June-August; HR 1.02; 95%CI: 1.01-1.04).

CONCLUSION

In this large-scale nationwide cohort study, we found a higher risk of AIT when born in the summer season or more specifically in June, supporting the hypothesis that seasonal variations in exposures-gestationally and/or early postnatally-may contribute to the development of AIT.

Are Perinatal Events Risk Factors for Childhood Thyroid Autoimmunity?

BACKGROUND

Environmental and genetic factors possibly trigger thyroid autoimmunity. Studies on perinatal risk factors for childhood thyroid autoimmunity are sparse.

OBJECTIVES

The aim was to investigate if perinatal factors, family history of autoimmune diseases, and HLA-DQ genotypes contribute to thyroid autoimmunity in the Diabetes Prediction in Skåne (DiPiS) study.

METHODS

Samples from 1,874 ten-year-old children were analyzed for autoantibodies to thyroid peroxidase (TPOAb), thyroglobulin (TGAb), and HLA-DQ genotypes. Information on perinatal events and family history of autoimmunity was gathered prospectively in questionnaires.

RESULTS

Thyroid autoimmunity was found in 6.9% of the children (TPOAb 4.4%, TGAb 5.8%, both autoantibodies 3.3%) and was overrepresented in girls. Prematurity was positively related to TGAb (OR: 2.4, p = 0.003, p_c = 0.021). Autoimmune diseases in the family increased the risk of thyroid autoimmunity: TPOAb (OR: 2.2, p = 0.012), any autoantibody (OR: 1.7, p = 0.04), and both autoantibodies (OR: 2.2, p = 0.024). A first-degree relative (FDR) with thyroid disease increased the risk for TPOAb (OR: 2.4, p = 0.03) and both autoantibodies (OR: 2.6, p = 0.03), a FDR or sibling with celiac disease increased the risk for both autoantibodies (OR: 3.7, p = 0.03, and OR: 4.8, p = 0.003), a FDR or sibling with diabetes increased the risk for thyroid autoantibody (OR: 3.0, p = 0.01, and OR: 5.4, p = 0.032), and a father with rheumatic disease increased the risk for TPOAb (OR: 15.2, p = 0.017), TGAb (OR: 11.3, p = 0.029), any autoantibody (OR: 9.6, p = 0.038), and both autoantibodies (OR: 20, p = 0.01).

CONCLUSIONS

Thyroid autoimmunity was found in 6.9% of the 10-year-old children who were being followed for their risk of type 1 diabetes. No relation to perinatal factors was found, with the exception of a possible association between prematurity and TGAb. Family history of autoimmune diseases increased the risk of thyroid autoimmunity.

Impact of Month of Birth on the Risk of Development of Autoimmune Addison's Disease

CONTEXT

The pathogenesis of autoimmune Addison's disease (AAD) is thought to be due to interplay of genetic, immune, and environmental factors. A month-of-birth effect, with increased risk for those born in autumn/winter months, has been described in autoimmune conditions such as type 1 diabetes and autoimmune thyroid disease.

OBJECTIVE

Month-of-birth effect was investigated in 2 independent cohorts of AAD subjects.

DESIGN, SETTING, AND PATIENTS

The monthly distribution of birth in AAD patients was compared with that of the general population using the cosinor test. A total of 415 AAD subjects from the United Kingdom cohort were compared with 8 180 180 United Kingdom births, and 231 AAD subjects from the Polish cohort were compared with 2 421 384 Polish births.

MAIN OUTCOME MEASURES

Association between month of birth and the susceptibility to AAD.

RESULTS

In the entire cohort of AAD subjects, month-of-birth distribution analysis showed significant periodicity with peak of births in December and trough in May (P = .028). Analysis of the odds ratio distribution based on month of birth in 2 cohorts of patients with AAD versus the general population revealed a December peak and May trough, and January peak and July trough, in the United Kingdom and Polish cohorts, respectively.

CONCLUSION

For the first time, we demonstrate that month of birth exerts an effect on the risk of developing AAD, with excess risk in individuals born in winter months and a protective effect when born in the summer. Exposure to seasonal viral infections in the perinatal period, coupled with vitamin D deficiency, could lead to dysregulation of innate immunity affecting the risk of developing AAD.

Impact of the birth's season on the development of celiac disease in Italy

Celiac disease (CD) is an immune-mediated systemic disorder induced by a trigger factor in genetically susceptible individuals. There is emerging evidence about the impact of the month of birth on the development of several autoimmune diseases. Our aim was to investigate whether, in Italian CD children, the season of birth is associated with development of CD later in life. We report a survey conducted at two Italian referral centers for CD in Rome and Bari. The CD database was created to enable retrospective examination of the data of all the consecutive patients, born between 2003 and 2010, who had received a diagnosis of CD. This CD patient group comprising 596 children was compared with a reference group that included all subjects born in the same period and in the same cities (439,990 controls). Overall, there was a summer birth preponderance in CD patients compared to controls (28.2 % of CD patients vs 23.0 % of the control population; OR 1.315; 95 % CI 1.100 to 1.572). Stratifying the caseload by gender and age, the summer birth preponderance was maintained for females (28.6 % CD females vs 22.6 % control females; OR 1.368; 95 % CI 1.069 to 1.750).

CONCLUSIONS

our survey confirms that in Italy, children born in summer are at higher risk to develop CD than subjects born in other seasons. The identification of a responsible seasonal factor or factors, such as timing of the first introduction of gluten and/or acute viral gastrointestinal infections, would be very important for disease prevention strategies.

WHAT IS KNOWN

• Environmental factors could be involved in the pathogenesis of CD. • Data about the impact of season of birth on CD development is so far derived from North American, Northern European and Israeli surveys.

WHAT IS NEW

• This is the first study in Southern Europe to find a relationship between season of birth (summer) and development of CD. • Summer-born infants are introduced to complementary feeding (gluten) in winter, when the rotavirus infection is at its highest peak; this may be the link between season of birth and development of CD.

The Pathogenesis of Hashimoto's Thyroiditis: Further Developments in our Understanding

Hashimoto's thyroiditis (HT) is part of a spectrum of thyroid autoimmune conditions and this review provides an update on the latest developments in the field. HT has a genetic predisposition with a number of immune-related and thyroid-specific genes conferring disease susceptibility. However, disentangling genes with protective and predisposing effect is a complex process that requires further work. The recent increase in the incidence of HT implicates environmental factors in disease pathogenesis including improved hygiene, increased dietary iodine intake, new treatment modalities and chemical agents. Additional unmodifiable predisposing factors include stress, climate, age and gender. Both cellular and humoral immunity play a role in HT pathogenesis. Defects in T regulatory cells and increased activation of follicular helper T cells may have a role in disease initiation/perpetuation. Infiltrating lymphocytes can be directly cytotoxic to thyroid follicular cells (TFC) or may affect cell viability/function indirectly through cytokine production, which alters TFC integrity and modulates their metabolic and immune function. Thyroid peroxidase and thyroglobulin antibodies are present in the majority of HT patients and help with management decisions. Antibodies against the sodium iodide symporter and pendrin are present in a minority with little known about their clinical relevance. In addition to immune cells, recent work has identified DNA fragments, generated following cell death, and micro RNA as potential factors in HT pathogenesis. Despite the large number of studies, the mechanistic pathways in HT are still not fully understood and further work is required to enhance our knowledge and identify novel preventative and therapeutic clinical targets.

Role of genetic and non-genetic factors in the etiology of Graves' disease

In spite of the advancements in understanding the pathogenic mechanisms of Graves' disease (GD), its ultimate cause remains elusive. The majority of investigators agree that GD is likely a multifactorial disease, due to a complex interplay of genetic and non-genetic factors that lead to the loss of immune tolerance to thyroid antigens and to the initiation of a sustained autoimmune reaction. Twin and family studies support a role of genetic factors, among which the HLA complex, CD40, CTLA-4, PTPN22, FCRL3, thyroglobulin, and the TSH receptor may be involved. Among non-genetic factors, iodine, infections, psychological stress, gender, smoking, thyroid damage, vitamin D, selenium, immune modulating agents, and periods of immune reconstitution may contribute the development of the diseases. Here we review in detail the respective role of genetic and non-genetic factors in the etiology of GD, taking advantage of the great bulk of data generated especially over the past 30 years.