The screening for mutations in the thyroglobulin cDNA from six patients with congenital hypothyroidism

The six patients described in this study were clinically diagnosed with con genital hypothyroidism. Based on clinical and pathophysiological parameters , the cause of the thyroid dyshormonogenesis was suspected to be a defect i n the synthesis of thyroglobulin, the matrix protein for thyroid hormone sy nthesis in the thyroid gland. After RNA isolation from six goitrous tissues and control thyroid tissues, RT-PCR was used to amplify 20 overlapping thy roglobulin (TG) cDNA fragments. Two alternative splice transcripts were ide ntified: a transcript with a deletion of nucleotides 177-274 and a transcri pt with a deletion of nucleotides 3430-3736 that result in frame shifts and the introduction of premature stop codons. Two alternatively spliced trans cripts not changing the reading frame were also identified: a transcript co ntaining a deletion of nucleotides 4529-4699 and a transcript with a deleti on of nucleotides 7301-7561. All these transcripts were expressed in thyroi d tissue of both patients and controls. Nucleotide sequence analysis and co mparison to the revised TG sequence (1997) revealed one revision and eight polymorphisms that did not result in amino acid changes and four polymorphi sms that did change amino acid codons. In three patients a homozygous mutat ion was present at nucleotide position 229, causing a glycine to serine ami no acid substitution. The clinical description 'thyroglobulin synthesis def ect' in this population cannot be explained by major mutations in the codin g region of the TG gene. Furthermore, the presence and level of expression of the alternatively spliced transcripts do not co-segregate with thyroid d yshormonogenesis, since in normal thyroid tissue the same alternatively spl iced transcripts are present. (C) Societe francaise de biochimie et biologi e moleculaire / Elsevier, Paris.