DIO1 and hypothyroidism: Second, simulations of both treatment strategies show that the L-T3/L-T4 combined therapy is slightly superior to treat hypothyroidism compared to the L-T4 monotherapy both in case without genetic variants and for genotype AA of polymorphism rs2235544 of gene DIO1. However, given genotype CC of polymorphism rs2235544, an L-T4 monotherapy can turn out to be advantageous compared to an L-T3/L-T4 combined therapy.