Thyroid peroxidase (TPO) is the key enzyme in the synthesis ofthyroid hormones, and the TPO defects are believed to be the most prevalent causes of the inborn errors of thyroid metabolism. We investigated an adopted boy with iodide organification defect, who presented with florid hypothyroidism at the age of4 mo, poorly complied with thyroxine treatment, and developed a compressive goiter necessitating partial resection at the age of 12 yr.Biochemical studies revealed the absence ofTPO activity in the resected tissue. Genomic DNA studies identified a 4 basepair insertion in the eighth exon of the TPO gene, and showed that the patient was homozygous for this frameshift mutation. The direct genetic diagnosis of this mutation can be made by digestion of polymerase chain reaction products with NaeI restriction enzyme. This will help assessing its prevalence among the heterogenous genetic group of TPO defects. (J. Clin. Invest. 1992. 90:1200-1204.) Key words: alternative splicing.

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These obtained in vitro results are the first effectiveness factors determined for human melanoma at the RA-3 nuclear reactor and show that BNCT dosimetry planning for patients could be successfully performed using these new factors.