[Clinical and molecular study of five families with resistance to thyroid hormones]

Thyroid hormone resistance and its management

The syndrome of impaired sensitivity to thyroid hormone, also known as syndrome of thyroid hormone resistance, is an inherited condition that occurs in 1 of 40,000 live births characterized by a reduced responsiveness of target tissues to thyroid hormone due to mutations on the thyroid hormone receptor. Patients can present with symptoms of hyperthyroidism or hypothyroidism. They usually have elevated thyroid hormones and a normal or elevated thyroid-stimulating hormone level. Due to their nonspecific symptomatic presentation, these patients can be misdiagnosed if the primary care physician is not familiar with the condition. This can result in frustration for the patient and sometimes unnecessary invasive treatment such as radioactive iodine ablation, as in the case presented herein.

Conservative management of pregnancy in patients with resistance to thyroid hormone associated with Hashimoto's thyroiditis

BACKGROUND

Resistance to thyroid hormone (RTH) is a rare thyroid disorder characterized by elevated free thyroid hormones with non-suppressed thyrotropin (TSH). Guidelines for the management of pregnancy in patients with RTH are not well defined. Chorionic villus biopsy is sometimes proposed to manage treatment based on the genotype of the fetus.

PATIENT FINDINGS

A woman with RTH (c1243C>T, pR320C mutation in the thyroid hormone receptor β (THRB gene)) associated with Hashimoto's thyroiditis (HT) had three successful pregnancies. During the pregnancies, the mother was treated with levothyroxine (LT4). She never underwent chorionic villus sampling. The babies had normal birth weights. The first child harbored the THRB mutation.

SUMMARY AND CONCLUSIONS

The management of pregnancies in patients with RTH and the indication for chorionic villus sampling are discussed in these cases. In RTH patients, pregnancies must be planned and closely followed. There is no need for prenatal diagnosis of RTH if the patient, due to limited thyroidal reserve, cannot produce excess of thyroid hormones to harm a normal fetus. The more common challenge in RTH remains how to best manage high maternal thyroid hormone levels, and whether or not to lower thyroid hormone levels based on the genotype of the fetus.

Identification of four novel mutations in the thyroid hormone receptor-β gene in 164 Spanish and 2 Greek patients with resistance to thyroid hormone

OBJECTIVE

The aim of the study was to describe the clinical, biochemical, and genetic features of a sample of Mediterranean patients with RTH (resistance to thyroid hormone) due to mutations in TRβ (thyroid hormone receptor beta) referred to our institution during the last 15 years.

DESIGN

166 blood samples were received for RTH genetic testing between January 1997 and December 2011. Genetic testing was performed by PCR amplification followed by sequencing of exons 7, 8, 9, and 10. Clinical and biochemical features were obtained from available information sent by referring hospitals.

RESULTS

Mutations were identified in 50 patients (29 probands and 21 relatives). 64% were women, and mean ± stdev age at diagnosis among probands was 33.2 ± 20.5 years. The following clinical features were recorded: goiter in 50%, hyperkinetic behavior in 32%, and tachycardia in 29%. Up to 19% of the probands had undergone some type of thyroidal ablative therapy before diagnosis. As for biochemical features, mean ± stdev TSH was 10.2 ± 21.4 mUI/L, and mean ± stdev fT4 was 35.5 ± 10.8 pmol/L. We found four new mutations: p.Phe451Leu, p.Pro452Arg, p.Glu457Gly, and p.Phe459Leu.

CONCLUSIONS

The clinical and biochemical characteristics of our samples of Mediterranean populations with RTH were similar to those described in the published literature. Interestingly, in our populations we have identified four novel mutations in the TRβ gene.