A de novo L330S point mutation in thyroid hormone receptor beta gene in a thai female with resistance to thyroid hormone

In the present study, we report a Thai female with a de novo mutation in th yroid hormone receptor-beta (TR beta) gene causing resistance to thyroid ho rmone (RTH). The patient was a 19 year-old woman who presented with goiter for 1 year. Except for tachycardia she had no signs of thyrotoxicosis. Prev iously she was treated with propylthiouracil based on the diagnosis of thyr otoxicosis for 9 months and her goiter became more enlarged. The patient wa s the only child of the family. Her parents were alive and healthy, and did not have goiter or any other thyroid diseases. Physical examination reveal ed no sign of thyrotoxicosis. Her thyroid gland was diffusely enlarged with an estimated weight of 100 gm. Laboratory determinations revealed elevated free T4, T3 and nonsuppressed TSH levels. Exon 9 of the TR beta gene was a mplified by PCR and the DNA sequence was determined by dye terminator cycle sequencing. Heterozygous point mutation in which T was replaced by C was d etected at position 1274 (TTG to TCG) corresponding to a leucine to serine: substitution at codon 330. No mutation was found in the parents indicating that the mutation was de novo. :The nucleotide change created a restrictio n site for Tag 1 restriction endonuclease and the mutation was confirmed by restriction fragments length polymorphism. The same nucleotide change has been reported in a family with RTH.