Discussion:
Resistance to thyroid hormone was first described as a clinical entity in 1967 [7]. Subsequent studies about the molecular pathogenesis of this syndrome identified mutations in the region of the gene that encodes the ligand-binding domain of THRb. Interestingly, patients with mutations in THRa  were not identified until 2012 [6]. Our patient in this article was found to have mutation in THRb same as majority of the patients described in the literature.
Patients with RTHb may have some symptoms or signs of hypothyroidism or hyperthyroidism, but these are variable and, when present, often inconstant. They frequently have elevated thyroid hormones level, high or normal TSH and goiter which suggest the importance of THRb in feedback of hypothalamic pituitary axis [6]. In contrast, patients with RTHa present with musculoskeletal and gastrointestinal abnormalities. They usually have near normal thyroid function due to lack of THRa contribution in feedback on hypothalamic pituitary axis [8,9]. Our patient initially presented with symptoms of hypothyroidism including weight gain and generalized fatigability in addition to high TSH which is consistent to typical presentation found in the literature. However, she had normal T3 and T4 which is not usually typical in presentation of RTHb that made our initial impression to be subclinical hypothyroidism.
To date, more than 100 THRB  mutations have been reported among RTH patients. Most mutations substitute a single amino-acid residue in the ligand-binding domain [10]. The most unique part in our case is found in genetic study, which confirmed that the patient is heterozygous in THRb gene for sequence variant designatedc.1147C>T , which is predicted to result in amino acid substitution p.Arg383Cys. this variant appears to have been reported in French patient with thyroid hormone resistant [11]. It was also reported in another affected individual but was inherited from apparently unaffected father [10]. Another variant affecting the same amino acid have also been reported in patient with thyroid hormone resistance [12].