A 138-nucleotide deletion in the thyroglobulin ribonucleic acid messenger in a congenital goiter with defective thyroglobulin synthesis.

Abstract

Two siblings (HSN and AcSN) with congenital goitrous hypothyroidism were investigated in terms of clinical, biochemical, and molecular biology. Diagnosis of defective thyroglobulin (Tg) was based on findings of low serum T4, low normal or normal serum T3, a negative percholate discharge test, and the virtual absence of the serum Tg response to challenge by bovine TSH. Only minute amounts of Tg-related antigens were detected by RIA in the goitrous tissue (HSN, 0.82 mg/g, compared to 70-90 mg/g in normal thyroid tissue), as confirmed by sodium dodecyl sulfate-agarose gel electrophoresis that indicated the virtual absence of Tg. The Tg messenger ribonucleic acids (mRNAs) from controls and HSN thyroid tissue were first reverse transcribed and then divided into several portions from positions 57-8448; the resulting complementary DNAs were, in turn, amplified by reverse polymerase chain reaction. The amplification of nucleotides 5165-6048 from control thyroid tissue Tg mRNA showed a fragment of 884 base pairs (bp). In contrast, the fragment present in the HSN was +/- 750 bp and lacked the normal fragment. The sequencing of the smaller fragment revealed that 138 bp were missing between positions 5590-5727 of the HSN Tg mRNA. This deletion does not affect the reading frame of the resulting mRNA and is potentially fully translatable into a Tg polypeptide chain that is shorter by 46 residues. A cysteine residue is maintained by the junction between the proximal T from leucine 1831 and the distal GT from cysteine 1877. DNA genomic polymerase chain reaction amplification excludes a deletion in the Tg gene and indicates that the deleted 138-nucleotide sequences lie in the same exon. The functional consequences of the deletion are not entirely clear, but it is conceivable that the excision of this segment of the Tg molecule could affect the protein structure, resulting in its premature degradation, very low colloid storage, and diminished thyroid hormone production rate.

A molecular analysis and long-term follow-up of two siblings with severe congenital hypothyroidism carrying the IVS30+1G>T intronic thyroglobulin mutation

“…The IVS30+1G>T mutation is caused by guanine to thymine transversion at position +1 in the donor splice site of intron 30. This mutations were previously identifi ed by our group in other two siblings from a not related family from the Northeast of Brazil (6). It was also confi rmed the compound heterozygous constellation IVS30+1G>T/A2215D in the two fi rst degree cousins of the siblings patients of the present study (8).…”

“…It was also confi rmed the compound heterozygous constellation IVS30+1G>T/A2215D in the two fi rst degree cousins of the siblings patients of the present study (8). This intronic mutation promotes aberrant splicing and loss of 138 nucleotides of the TG mRNA, removing the entire exon 30 (6,7). Elimination of this exon does not affect the reading frame of the mRNA and potentially codifi es a shortened polypeptide.…”

“…Thirty-eight inactivating mutations have been identifi ed, characterized in the human TG gene and associated to congenital goiter and hypothyroidism (5). We have previously identifi ed the intronic IVS30+1G>T mutation in two Brazilian families with a complex history of fetal goiter and congenital goiter, born to consanguineous parents (6)(7)(8). In this report we have extended our initial molecular and immunlogic studies of two affected goitrous siblings with defective TG synthesis and we describe the eleven year follow-up of the two siblings harboring this mutation.…”

A novel compound heterozygous mutation in the thyroglobulin gene resulting in congenital goitrous hypothyroidism with high serum triiodothyronine levels

“…There are three types of repetitive units in the thyroglobulin protein, and residue Cys1897 is located in repeated motif type 3a (Malthiery and Lissitzky 1987). Another family with an in-frame deletion mutation in this domain has been reported (Targovnik et al 1995). The type 3 repeated motif might be important for thyroglobulin, but its function remains unknown.…”

“…The prevalence of patients with thyroglobulin defects is 1:40,000-100,000 newborns. However, due to the difficulty of analyzing large genes, only nine different mutations leading to congenital goiter and hypothyroidism have thus far been identified in the human thyroglobulin gene (Ieiri et al 1991;Targovnik et al 1993Targovnik et al , 1995van de Graaf et al 1999;Hishinuma et al 1999;Caron et al 2003;Gutnisky et al 2004).…”