Subclinical hyperthyroidism is defined as low or undetectable concentration of serum thyrotrophin (TSH) with normal free triiodothyronine (FT3) and free thyroxine (FT4) levels. 1). Familial subclinical hyperthyroidism is a rare entity. Activating mutations of the TSH receptor (TSH-R) gene cause genetic hyperthyroidism. Here we present a family with more than one affected individual. All family members were investigated for TSH-R mutation. No mutation was detected, while a A459 polymorphism was found in one of the cases and three other siblings. Despite the clinical and biochemical findings suggesting a TSH-R mutation, a reasonable cause could not be detected. Epigenetic and environmental modifiers, including iodine intake, should be considered in families with mutation negative, familial non auto-immune hyperthyroidism (FNAH).
Key words: Familial, Subclinical Hyperthyroidism, Genetics
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