One hypothesis is that a SNP (Thr92Ala) in DIO2 (required for local production of T3 out of T4) interferes with its kinetics and/or action, resulting in a local hypothyroid state in the brain.
Thyroidectomized patients carrying Thr92Ala are at increased risk of reduced intracellular and serum T3 concentrations that are not adequately compensated for by LT4, thus providing evidence in favor of customized treatment of hypothyroidism in athyreotic patients.
The present study indicates that the combination of polymorphisms in <i>DIO2</i> (rs225014) and <i>MCT10</i> (rs17606253) enhances hypothyroid patients' preference for L-T4 + L-T3 replacement therapy.
A polymorphism (Thr92Ala) in the gene encoding the deiodinase 2 (D2) enzyme that converts thyroxine to triiodothyronine in the brain was later identified in about 16% of hypothyroid persons.