This gets a little technical but it is another step in knowledge about polymorphisms. Full free PDF is available. PR
"Hypothyroidism is found in about 4.6% of the U.S. population age 12 and older (1). The current standard
of care for these patients is treatment with daily tablets of the long-lived prothyroid hormone (TH), levothyroxine (L-T4). T4 is subsequently activated to T3 outside of the thyroid parenchyma via the deiodinases, ie, D1 and D2. Unfortunately therapy with L-T4 alone does not resolve symptoms in all hypothyroid patients, with approximately 12% of the patients remaining symptomatic despite normalization of serum TSH and TH levels (2, 3). Impaired cognition, fatigue and difficulty losing weight
are the main residual symptoms of these patients, for which we lack understanding and have no mechanistic explanation."