Is FOXE1 rs965513 AA associated with altered thyroid development and thyroid-axis traits?

The FOXE1 rs965513 AA genotype is a well-established genetic modifier that alters thyroid morphogenesis and systemic thyroid-axis regulation. Rather than driving direct thyroid-stimulating hormone (TSH) elevation, this variant introduces inherited vulnerability by shifting baseline physiological set-points.

Thyroid-axis set-points

• TSH reduction: Large-scale population and neonatal studies demonstrate that the rs965513 risk A allele is associated with lower, rather than elevated, circulating TSH levels. Each copy of the A allele decreases serum TSH by approximately 5.9% in euthyroid individuals, accompanied by subtle shifts in free thyroxine ($T_4$) and triiodothyronine ($T_3$) profiles.
• Baseline vulnerability: The AA genotype represents an inherited vulnerability that alters baseline thyroid-axis traits (neonatal and adult TSH, free T4) without serving as a direct driver of isolated, high-TSH clinical phenotypes.

Molecular and epigenetic mechanisms

• Enhancer downregulation: Located within an upstream long-range enhancer region on chromosome 9q22.33, the rs965513 AA genotype reduces chromatin activity and transcription factor binding in unaffected thyroid tissues.
• Target gene suppression: This regulatory disruption downregulates the expression of the thyroid-specific transcription factor FOXE1, the long non-coding RNA PTCSC2, and the TSH receptor (TSHR).
• Feedback loop modification: Decreased expression of TSHR alters the baseline feedback sensitivity of the thyroid-stimulating hormone axis, establishing a lower set-point for systemic TSH levels.

Clinical implications and pathology

• Oncogenic susceptibility: Beyond its role in functional thyroid-axis set-points, the rs965513 A allele is highly associated with structural susceptibility, acting as a robust risk locus for differentiated and papillary thyroid carcinoma (PTC).

Bottom line

• The FOXE1 rs965513 AA genotype alters early thyroid development and shifts the baseline thyroid-axis set-point downward—reducing TSH by approximately 5.9% per allele—via the transcriptional downregulation of FOXE1, TSHR, and PTCSC2. While it does not drive elevated TSH, it introduces an inherited thyroid-axis vulnerability and increases susceptibility to papillary thyroid carcinoma.