[Thyroglobulin (Tg) gene and familial Tg synthesis defect]

The thyroglobulin (Tg) gene is a 300-kilobase (kb) single copy gene, containing at least 42 exons, mapped in man to chromosome 8 (8q24) and codes for a glycoprotein with a molecular weight 660,000, which functions as a matrix for the thyroid hormone (T4, T3) and iodothyronine synthesis. Recent progress in genetic technology enables us to study a family case of hereditary goiter with hypothyroidism due to Tg synthesis defect. RT-PCR and subsequent sequencing of the Tg gene revealed a C to G conversion at -3 position of the acceptor splice site in intron 3. This splice site mutation resulted in exon. 4-deleted (major) and exon 3-5-deleted (minor) mRNAs in the goiter thyroid. This defect in this patient indicates the importance of the tyrosine No. 130, coded within the exon 4, in the thyroid hormone formation.