An identical neo-mutation in the thyroid hormone receptor beta gene (A317T) in 2 unrelated Thai families with resistance to thyroid hormone.

We reported two unrelated Thai girls with resistance to thyroid hormone. The affected patients presented with goiter and no other stigmata of hyperthyroidism. Their serum T4. T3. free T 4 and free T 3 concentrations were high and they had normal levels of TSH. The affected girl in family 1 was treated with an antithyroid drug for 1-9112 years. The affected girl in family 2 was only observed her thyroid function tests. TRH test showed normal TSH response in both girls. Analysis of the thyroid hormone receptor B gene of both affected girls revealed the same missense mutation, changing the guanine in nucleotide 1234 to an adenine which results in the replacement of the normal alanine (OCT) with a threonine (ACT) at codon 317. Two proposita were heterozygous, and this mutation was not present in their parents compatible with a neo- mutation. Key word : Resistance to Thyroid Hormone, Two Unrelated Thai Families