There are studies that investigate the potential impact of exposure to PFAS (and to PFOA specifically) on thyroid hormone levels (e.g., triiodothyronine, T3; thyroxine, T4) and thyroid-stimulating hormone (TSH), and also on diagnosed specific thyroid diseases (e.g., hypothyroidism or hyperthyroidism). This evidence concerns the gene TG and thyroid gland disorder.