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Division of Endocrinology and Metabolism, Department of Internal Medicine, Philipps University (W.J., A.E.H.), D-35033 Marburg; and Städtisches Klinikum Leipzig-West (T.M., K.H., M.K., H.-J.H.), D-04177 Leipzig, Germany
Address all correspondence and requests for reprints to: Armin E. Heufelder, M.D., Division of Endocrinology and Metabolism, Zentrum für Innere Medizin, Philipps University, Baldingerstrasse, D-35033 Marburg, Germany. E-mail: heufeld{at}mailer.uni-marburg.de
| Abstract |
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| Introduction |
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| Subjects and Methods |
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Investigations adhered to the tenets of the Declaration of Helsinki. Informed consent was obtained from the participants after the nature and possible consequences of the study had been explained to them. The research program was approved by the institutional human experimentation committees.
A total of 128 white German patients (31 men and 97 women) with scintigraphically proven thyroid autonomy, all native residents of Saxony, were genotyped for the codon 727 hTSHR polymorphism and compared with 99 healthy control individuals (31 men and 68 women) and 108 patients with GD (17 males and 91 females), all of whom were natives of the same geographic region. Thyroid hyperfunctioning nodules and GD were diagnosed by standard criteria (clinical examination, thyroid function tests, ultrasonography, TSHR and thyroid peroxidase antibody titers, and quantitative technetium scintigraphy). Patients with thyroid autonomy were divided into 3 subpopulations: those with solitary toxic adenoma (n = 83), those with toxic multinodular goiter (n = 31), and those with disseminated autonomy (n = 14). All healthy control participants had documented normal thyroid function and no evidence of thyroid autoimmune or nonautoimmune disease, as determined by a careful personal and family history, clinical examination, thyroid function, and thyroid autoantibody testing.
Polymorphism typing
Genomic DNA was extracted from ethylenediamine tetraacetate-anticoagulated peripheral blood. The polymorphic region within codon 727 of the hTSHR gene was amplified by PCR. Oligonucleotide primers used for analysis of mutant hTSHR gene expression were 5'-AACGCCAGGCTCAGGCATAC-3' and 5'-AAGTTCCCCTACCATTGTGA-3'. These primers should generate a product that is 232 bp in length. Amplifications were performed using 5 µL of each DNA template, 5 µL 10 x PCR reaction buffer, 1 µL 10 mmol/L deoxy-NTP, 0.6 µL of each oligonucleotide primer (50 µmol/L), and 2.5 U Taq DNA polymerase in a final volume of 50 µL. Amplifications were performed in an automated thermocycler (Thermodux, Wertheim, Germany) with 5 min of denaturation at 94 C, followed by 35 cycles of 45 s at 94 C, 1 min at 58 C, and 1 min at 72 C and a final 5-min extension at 72 C. Subsequently, restriction enzyme digestion was performed to distinguish mutant from wild-type hTSHR fragments. To this purpose, PCR transcripts were precipitated and resuspended in Aqua bidest. The restriction enzyme NlaIII (2.5 U) was used for hydrolysis in a final volume of 36 µL of the appropriate buffer. After incubation at 37 C for 1 h, digested fragments were resolved on 3% NuSieve agarose gels containing 10 mg/ml ethidium bromide, visualized by UV light, and compared with a 100-bp molecular size control ladder. The mutation at position 727 of the hTSHR gene alters the restriction site for NlaIII, producing two DNA fragments from the amplicon rather than three generated with wild-type DNA. Thus, the wild-type strand produces fragments of 129, 82, and 21 bp, whereas the codon 727 mutant DNA produces fragments of 129 and 103 bp, respectively.
Sequencing
To confirm wild-type sequence or point mutation, respectively,
PCR products of several homozygous and heterozygous individuals were
resolved on an ethidium bromide-stained agarose gel. DNA fragments were
excised, isolated, and ligated overnight at 16 C into the DNA-plasmid
pCR (Invitrogen, Groningen, The Netherlands). Using
the Easyject Plus Electroporation System (Eurogentec, Seraing,
Belgium), transfection of competent Escherichia coli
XL1-blue cells was performed. Plasmid DNA of three picked clones was
purified with QIAGEN-tip 20 (QIAGEN, Hilden, Germany) and sequenced
with a Sequenase kit (version 2.0, U.S. Biochemical Corp.,
Cleveland, OH) using [
-35S]deoxy-ATP for
labeling. The reaction mixes were then run on denaturing 6% (wt/vol)
polyacrylamide-7 mol/L urea gels and exposed to x-ray films.
Statistical analysis
Allelic frequencies (number of copies of a specific allele divided by total number of alleles in the group) were calculated for the study groups. Statistical significance was determined using Fishers exact test. P < 0.05 indicated a statistically significant difference. Data were analyzed using InStat 3.00 for Win 3.1 (1997) software (GraphPad Software, Inc., San Diego, CA).
| Results |
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| Discussion |
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-subunit
of the stimulatory G protein (Gs
) have been
implicated as major causes of thyroid hyperfunctioning adenomas (4, 7, 8, 9). Recently, Morris et al. reported a surprisingly high
frequency of a germline polymorphism of codon 727 of hTSHR in patients
with toxic multinodular goiter, suggesting that it may be a
predisposing factor in toxic multinodular goiter (5). Functional
analysis of the codon 727 polymorphism of the hTSHR revealed a
significantly greater cAMP response of the mutant hTSHR to TSH
stimulation than wild-type receptor, although basal cAMP production
levels were similar (5). However, these data have been contradicted by
a recent study (10) in which the researchers were unable to detect any
significant difference in activation of the cAMP cascade between
wild-type TSH receptor and the variant D727E TSH receptor. Moreover, in
contrast to the data reported by Gabriel et al. (5), we
failed to detect a significant difference in codon 727 polymorphism
between patients with toxic multinodular goiter and the healthy control
group. Similarly, none of the other patient groups, including patients
with solitary toxic adenoma, disseminated autonomy, or GD, were related
to a significant difference in their codon 727 polymorphism frequencies
compared to the healthy control group. Several studies have recently
detected somatic activating mutations of the hTSHR gene in single
hyperfunctioning nodules contained in multinodular goiter (11, 12, 13, 14). It
is still debated whether an activating mutation of the hTSHR gene or
the Gs
gene is by itself sufficient to promote
the evolution of toxic adenomas and goiter nodules. Similar clinical
features in patients with thyroid hyperfunctioning adenomas with and
without hTSHR/Gs
receptor mutations have been
reported by Arturi et al. (15), suggesting that additional
mechanisms may contribute to the pathogenesis of toxic adenomas.
Moreover, the prevalence of somatic hTSHR mutations (ranging from
082%) and that of Gs
mutations (438%) is
still controversial (6, 16, 17). Differences in methodology,
recruitment, geographical origin of patients, and environmental
factors, such as iodine intake, may explain some of these
discrepancies. Although mutational activation of the adenylate cyclase
cascade has been experimentally shown to cause increased proliferation
and function of thyroid cells in vivo and in
vitro (18, 19), Derwahl et al. failed to establish any
correlation between basal or TSH-stimulated adenylate cyclase activity
and the levels of Gs
and
Gi
expressed by toxic adenomas with or without
activating mutations and in nodular and extranodular tissues of toxic
multinodular goiter with proven germline mutation in the hTSHR gene
(20). These data suggest that hTSHR and Gs
gene mutations alone may not be sufficient to cause hyperfunctioning
nonautoimmune thyroid disease. Low iodine intake in our European
Caucasian study population may be largely responsible for the
pathological thyroid conditions studied, thus explaining some of the
discrepancies of TSHR genotyping compared to the results of Gabriel
et al. (5), who studied individuals developing thyroid
abnormalities despite sufficient iodine supply. In conclusion, our
current data do not support an association between the codon 727
polymorphism of the hTSHR gene and hyperfunctioning thyroid
abnormalities in a European population. Thus, the codon 727 hTSHR gene
polymorphism does not appear to be involved in the evolution of toxic
nonautoimmune thyroid disease.
| Acknowledgments |
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| Footnotes |
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Received December 2, 1999.
Revised March 21, 2000.
Accepted March 29, 2000.
| References |
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protein gene
in 31 toxic thyroid nodules. J Clin Endocrinol Metab. 82:38853891.
. Mol Cell
Endocrinol. 138:137142.[CrossRef][Medline]
genes as a cause of toxic
thyroid adenomas. J Clin Endocrinol Metab. 82:26952701.
. Eur J Endocrinol. 138:3740.[Abstract]
stimulates growth
and differentiation of thyroid FRTL5 cells. Oncogene. 9:364753.[Medline]
protein-adenylate cyclase pathway may not be sufficient to generate
toxic thyroid adenomas. J Clin Endocrinol Metab. 81:18981904.[Abstract]
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