Clinical case seminar: metastatic follicular thyroid carcinoma arising from congenital goiter as a result of a novel splice donor site mutation in the thyroglobulin gene.
BACKGROUND
Defects in thyroglobulin (Tg) synthesis are one of the causes of thyroid dyshormonogenesis. Only a few mutations in the Tg gene have been described.


OBJECTIVE
We describe a novel Tg gene mutation and discuss the mechanisms by which it causes dyshormonogenesis with subsequent malignant transformation.


METHODS
Two siblings aged 21 and 19 yr presented with recurrent goiters for which they had undergone multiple thyroid surgeries since early childhood. The older sibling was diagnosed with metastatic follicular thyroid carcinoma at age 15 yr.


METHODS
The entire coding region and intron-exon boundaries of the Tg gene were amplified and sequenced from the patients. We also sequenced the boundaries of exon 5 and intron 5 from both parents. RT-PCR amplification of a cDNA fragment encompassing exons 4-6 was also performed.


RESULTS
A homozygous G to A point mutation at position +1 of the splice donor site of intron 5 (g.IVS5+1G-->A) was detected in both patients, whereas a monoallelic mutation was found in their parents. RT-PCR amplification of a cDNA fragment covering exons 4-6 revealed a 191-bp fragment in the patients and 351- and 191-bp fragments in the parents. Sequence analysis of these two fragments confirmed deletion of exon 5 in the 191-bp fragment.


CONCLUSIONS
Aberrant splicing occurred as a result of the g.IVS5+1G-->A mutation, which caused fusion of exons 4 and 6, resulting in the frame shift at codon position 141 and a premature stop codon at position 147 (FS141-->147X). The malignant transformation is likely a result of prolonged TSH stimulation.
Alzahrani
Ali S
AS
Department of Medicine, King Faisal Specialist Hospital and Research Centre, P.O. Box 3354, Riyadh 11211, Saudi Arabia.
Baitei
Essa Y
EY
Zou
Minjing
M
Shi
Yufei
Y
D018263:Adenocarcinoma, Follicular / Q000209:etiology*; D000328:Adult; D017398:Alternative Splicing; D005260:Female; D016368:Frameshift Mutation; D006042:Goiter / Q000150:complications* / Q000151:congenital / Q000235:genetics; D006801:Humans; D008297:Male; D010375:Pedigree; D013954:Thyroglobulin / Q000235:genetics*; D013964:Thyroid Neoplasms / Q000209:etiology*
D013954:Thyroglobulin