An Identical Neo-mutation in the Thyroid Hormone
Receptor 6 Gene (A317T) in 2 Unrelated Thai Families
with Resistance to Thyroid Hormone
THONGKUM SUNTHORNTHEPVARAKUL, M.D.*, SOMCHIT JARURATANASIRIKUL, M.D.**,
SUPAWADEE LIKITMASKUL, M.D.***,
KITTI ANGSUSINGHA, M.D.***,
SUPUNNEE NGOWNGARMRATANA, M.D.*
Affiliation : * Department of Medicine, Rajavithi Hospital, Bangkok 10400,
**Department of Pediatrics, Faculty of Medicine, Prince of Songkla University, Hat Yai, Songkhla 90110,
*** Department of Pediatrics, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand.
AbstractWe 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.
Keywords : Resistance to Thyroid Hormone, Two Unrelated Thai Families
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