Skewed X Chromosome Inactivation and Female Preponderance in Autoimmune Thyroid Disease: An Association Study and Meta-Analysis

Context: A number of small data sets have suggested a potential role for skewed X chromosome activation (XCI), away from the expected 50: 50 parent of origin ratio, as an explanation for the strong female preponderance seen in the common autoimmune thyroid diseases (AITD), Graves' disease (GD), and Hashimoto's thyroiditis (HT). Objective: The objective of the study was to confirm a role for XCI skewing as a potential explanation for the strong female preponderance seen in AITD. Design: The design of the study was to screen XCI in the largest GD, HT, and control case-control cohort and family cohort to date and undertake a meta-analysis of previous AITD XCI reports. Setting: The study was conducted at a research laboratory. Patients: Three hundred and nine GD, 490 HT, and 325 female UK Caucasians controls, 273 UK Caucasian GD families, and a meta-analysis of 454 GD, 673 HT, and 643 female Caucasian controls were included in the study. Main Outcome Measures: Case-control and family-based association studies and meta-analysis were measured. Results: Skewed XCI was observed with GD [odds ratio (OR) 2.17 [95% confidence interval (CI) 1.43-3.30], P = 2.1 x 10(-4)] and a trend toward skewing with HT(P = .08) compared with the control cohort. A meta-analysis of our UK data and that of four previous non-UK Caucasian studies confirmed significant skewing of XCI with GD [OR 2.54 (95% CI 1.58-4.10), P = 1.0 x 10(-4), I-2 = 30.2%] and HT [OR 2.40 (95% CI 1.10-5.26), P = .03, I-2 = 74.3%]. Conclusions: Convincing evidence exists to support a role for skewed XCI in female subjects with AITD, which may, in part, explain the strong female preponderance observed in this disease.