Congenital primary hypothyroidism occurs in 1 of 4000 births. Whereas the majority of the cases are due to developmental defects of the thyroid gland, 20% carry a defect in thyroid hormonogenesis. We report a Turkish boy who had goitrous hypothyroidism due to a mutation in the thyroid peroxidase (TPO) gene.
The TPO gene was sequenced directly from genomic DNA and cDNA which was transcribed from three RNA samples harvested from different parts of the patient's excised thyroid gland. Patient The boy was thyroidectomized because of continuing growth of his thyroid gland and development of multiple nodes suspected of malignancy by ultrasound examination. Histopathological examination verified a dyshormonogenetic goiter with multiple follicular adenomas.
The patient had a novel homozygous 10-bp deletion of the TPO gene at position 2812 in exon 16. This frame shift mutation results in a severely altered intracellular part of the protein. The deletion identified in leucocyte DNA was also found in thyroid tissue cDNA - so that instability of the transcript or a splicing defect was excluded. Both unaffected parents were heterozygous carriers of the mutation whereas 50 healthy individuals of the same ethnic background did not harbour the mutation.
The identified TPO gene deletion is the first mutation coding for an inactive TPO molecule, which has a severely altered intracellular segment. Because the most likely reason for the enlarging goiter was poor compliance of the patient, this report underlines the importance of a careful and regular follow-up of patients with dyshormonogenesis.
[Show abstract][Hide abstract] ABSTRACT: Thyroid dyshormonogenesis is a genetically heterogeneous group of inherited disorders in the enzymatic cascade of thyroid hormone synthesis that result in congenital hypothyroidism (CH). Thyroid peroxidase gene (TPO) mutations are one of the most common causes of thyroid dyshormonogenesis. The aim of this study was to identify TPO gene defects in a cohort of patients with thyroid dyshormonogenesis from Slovenia, Bosnia, and Slovakia.
Forty-three patients with permanent CH and orthoptic thyroid glands from 39 unrelated families participated in the study. Mutational analysis of the TPO gene and part of its promoter consisted of single-stranded conformation polymorphism analysis, sequencing, and restriction fragment length polymorphism (RFLP) analysis.
TPO gene mutations were identified in 46% of participants. Seven different mutations were identified, four mutations of these being novel, namely 613C > T (R175X), 1519_1539del (A477_N483del), 2089G > A (G667S), and 2669G > A (G860R). Only a single allele mutation was identified in 65% of the TPO mutation carriers.
The results showed a higher prevalence of TPO gene mutations in thyroid dyshormonogenesis when compared with published studies. The high percentage of single allele mutations implied possible intronic or regulatory TPO gene mutations or monoallelic expression.
European Journal of Endocrinology 06/2007; 156(5):511-9. DOI:10.1530/EJE-07-0037 · 4.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Iodide organification defects are frequently but not always associated with mutations in the thyroid peroxidase (TPO) gene and characterized by a positive perchlorate discharge test. These mutations phenotypically produce a congenital goitrous hypothyroidism, with an autosomal recessive mode of inheritance.
In the present study we extended our initial molecular studies in six unrelated patients heterozygous for the TPO mutations, in order to identify the second mutation in this autosomal recessive disease.
The promoter and the complete coding regions of the human TPO and DUOXA2 genes, along with the flanking regions of each intron were analysed by direct DNA sequencing.
Four different inactivating TPO mutations were identified in two patients: two novel mutations (c.215delA [p.Q72fsX86] and c.1159G-->A [p.G387R]) and two previously reported (c.387delC [p.N129fsX208] and c.2422T-->C [p.C808R]), confirming the inheritance of two different compound heterozygous mutations, c.215delA/c.2422T-->C and c.387delC/c.1159G-->A. The remaining four patients did not show additional inactivating mutations in the TPO gene and all had only the wild type sequencing in the DUOXA2 gene.
We have reported two patients with iodide organification defect caused by two compound heterozygous mutations, c.215delA/c.2422T-->C [p.Q72fsX86/p.C808R] and c.387delC/c.1159G-->A [p.N129fsX208/p.G387R], in the TPO gene and four patients with monoallelic TPO defect. Identification of the molecular basis of this disorder might be helpful for understanding the pathophysiology of congenital hypothyroidism.
[Show abstract][Hide abstract] ABSTRACT: Congenital primary hypothyroidism occurs in one out of 4,000 births. About 20% of cases are due to defects in thyroid hormonogenesis. We report on a German girl with congenital hypothyroidism due to a mutation in the thyroid peroxidase (TPO) gene who had elevated serum levels of thyroglobulin during periods of hyperthyrotropinemia.
The TPO gene was sequenced directly from genomic DNA.
The patient had a novel homozygous mutation (R314W) in the TPO gene. The unaffected parents were non-consanguineous and both heterozygous carriers of the mutation. Fifty normal individuals did not harbor the mutation ruling out a common polymorphism.
The identified TPO gene mutation (R314W) is very likely the genetic cause for hypothyroidism in the reported child. R314W has not been described before and codes for a presumably inactive TPO molecule.
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