Modification of TSH-related genetic effects by indicators of socioeconomic position

Objective: Thyroid-stimulating hormone (TSH) is influenced by genetic and environmental factors such as socioeconomic position (SEP). However, interactions between TSH-related genetic factors and indicators of SEP have not been investigated to date. Aim of the study was to determine whether education and income as SEP indicators may interact with TSH-related genetic effect allele sum scores (GESTSH_2013 and GESTSH_2020) based on two different GWAS meta-analyses to affect TSH values in a population-based study. 

Methods: In 4085 participants of the Heinz Nixdorf Recall Study associations between SEP indicators, GESTSH and TSH were quantified using sex- and age-adjusted linear regression models. Interactions between SEP indicators and GESTSH were assessed by GESTSH x SEP interaction terms, single reference joint effects and calculating genetic effects stratified by SEP group. 

Results: Participants within the highest education group showed the strongest genetic effect with on average 1.109-fold (95%-CI 1.067-1.155) higher TSH values per GESTSH_2013 standard deviation, while in the lowest education group the genetic effect was less strong (1.061-fold (95%-CI 1.022-1.103)). In linear regression models including interaction terms some weak indication for a positive GESTSH_2013 by education interaction was observed showing an interaction effect size estimate of 1.005 (95%-CI 1.000-1.010) per year of education and GESTSH_2013 standard deviation. No indication for interaction was observed for using income as SEP indicator. For using the GESTSH_2020 similar results were observed.

Conclusion: Our results gave some indication that education may affect the expression of TSH-related genetic effects. Stronger genetic effects in high education groups may be explained by environmental factors that have an impact on gene expression and are more prevalent in high SEP groups.