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X Chromosome Inactivation Pattern is not Associated With Interindividual Variations in Thyroid Volume: A Study of Euthyroid Danish Female Twins

Published online by Cambridge University Press:  21 February 2012

Thomas Heiberg Brix*
Affiliation:
Department of Endocrinology and Metabolism, Odense University Hospital, Denmark. [email protected]
Pia Skov Hansen
Affiliation:
Department of Endocrinology and Metabolism, Odense University Hospital, Denmark; The Danish Twin Registry, Epidemiology, Institute of Public Health, University of Southern Denmark, Odense, Denmark.
Finn Noe Bennedbæk
Affiliation:
Department of Endocrinology and Metabolism, Odense University Hospital, Denmark.
Steen Joop Bonnema
Affiliation:
Department of Endocrinology and Metabolism, Odense University Hospital, Denmark.
Kirsten Ohm Kyvik
Affiliation:
Institute of Regional Health Services Research, University of Southern Denmark, Odense, Denmark; The Danish Twin Registry, Epidemiology, Institute of Public Health, University of Southern Denmark, Odense, Denmark.
Karen Helene Ørstavik
Affiliation:
Faculty Division Rikshospitalet, University of Oslo, Oslo, Norway; Department of Medical Genetics, Oslo University Hospital, Rikshospitalet, Oslo, Norway.
Laszlo Hegedüs
Affiliation:
Department of Endocrinology and Metabolism, Odense University Hospital, Denmark.
*
*Address for correspondence: Thomas Heiberg Brix, Department of Endocrinology, Odense University Hospital, Sdr. Boulevard 29, 5000 Odense C, Denmark.

Abstract

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Ahigher frequency of skewed X chromosome inactivation (XCI) is found in patients with autoimmune thyroid disease (AITD) than in controls. Although goitre is often present in AITD, a recent study failed to show an association between XCI and clinically overt nontoxic goitre. However, the etiology of overt goitre is complex, and the mechanisms influencing thyroid volume may involve fewer factors than the mechanisms underlying overt goitre. In order to examine the impact of XCI on thyroid volume in euthyroid females, we studied whether within cohort (n = 138) and within twin pair (n = 69) differences in XCI are correlated with differences in thyroid volume. XCI was determined by PCR analysis of a polymorphic CAG repeat in the first exon of the androgen receptor gene. Thyroid volume was determined by ultrasound. Neither in the within cohort nor in the within twin pair analysis could we demonstrate a statistically significant association between XCI and thyroid volume: Regression coefficient (β) = 0.023 (95% confidence interval, –0.062–0.108), p = 0.592 and β = 0.038 (–0.080–0.156), p = 0.521, respectively. Controlling for potential confounders such as zygosity, age, TSH, smoking habits and use of oral contraceptives did not change the findings. In conclusion, in a sample of euthyroid Danish female twins, we found no evidence of a relationship between XCI pattern and thyroid volume.

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Articles
Copyright
Copyright © Cambridge University Press 2009