Causes are similar to those of overt hypothyroidism; most common being chronic autoimmune thyroiditis associated with anti-thyroid peroxidase antibodies (Hashimoto’s thyroiditis), whereas others include sub-acute thyroiditis, post-partum thyroiditis, previous hyperthyroidism, in association with other autoimmune diseases, thyroid injury/inflammation due to radiation, surgery, medication and thyroid infiltration.1 The gene discussed is TPO; the disease is hypothyroidism.