Previous studies have shown widely varying estimates of thyroid dysfunction incidence in patients with atrial fibrillation, probably resulting from the use of different methods for determining thyroid hormone levels, variation in diagnostic limits, and evaluation of different populations.5,7,21 Forfar et al.21 and Ciaccheri et al.22 described thyrotoxicosis prevalence of around 13%. The gene discussed is TG; the disease is atrial fibrillation.