Investigations include thyroid function tests [TSH, free T4 and free T3 (if strong clinical suspicion but normal TSH and free T4)], thyroid auto-antibodies (anti-TSH receptor, anti-thyroid peroxidase and anti-Tg antibodies), orbital imaging [magnetic resonance imaging (MRI) is better for identifying active disease (muscle bellies show inflammation and enlargement with spared tendons) whereas computed tomography (CT) is better for bone resolution when planning decompression surgery], visual field analysis, orthoptic assessment and optometric assessment. The gene discussed is TPO; the disease is thyroiditis.