A clinically euthyroid child with a large goiter due to a thyroglobulin gene defect: Clinical features and genetic studies

A 10-year old child born to consanguineous parents presented with an extremely large goiter, a low free T₄ level and free T₄ index, and normal TSH concentration. The findings of undetectable thyroglobulin (TG) and low free T₄, and an elevated free T₃/free T ₄ ratio suggested the possibility of a defect in TG synthesis. Noteworthy aspects of this case were the extremely elevated thyroidal radioiodide uptake despite a normal TSH concentration and the fact that the reduction in the size of her goiter only occurred when her TSH was suppressed below the normal range. Gene sequencing revealed that the patient was homozygous for a donor splice site mutation in intron 30 (IVS30+1G>C). Isolation of RNA obtained from the thyroid gland by fine needle aspiration and sequencing of the TG cDNA confirmed the prediction that exon 30 was skipped, resulting in an in-frame loss of 46 amino acids.