| Abstract: |
Background: Serum concentrations of some hormones are risk factors for certain cancers, but little is known about their familial associations especially for females. Methods: We measured serum concentrations of estradiol (E<sub>2</sub>), testosterone (T), SHBG, prolactin, and IGF-I for 645 Australian female postmenopausal twins and their sisters [182 monozygotic (MZ) and 107 dizygotic (DZ) pairs and 67 nontwin sisters] using well-established immunoassays. After suitable transformation and adjusting for age, body mass index (BMI), and time since menopause, familial correlations and proportions of variance attributed to genetic (h<sup>2</sup>) and nongenetic factors common to sisterships (c<sup>2</sup>) were estimated under the classic twin multivariate normal model using FISHER. Results: For all serum concentrations except prolactin, MZ, DZ, and sister pairs were correlated (P< 0.001). MZ correlations were in the range 0.5- 0.7, and for all serum concentrations, there were no differences between DZ and sister correlations. MZ correlations were greater than DZ and sister correlations for log SHBG (P = 0.0001), IGF-I (P = 0.0002), and square-root T (P = 0.007) but not log E<sub>2</sub> (P = 0.3), and the respective h<sup>2</sup> estimates were 0.56 (SE = 0.14), 0.53 (0.17), 0.39 (0.14), and 0.14 (0.16). For log E<sub>2</sub> and square-root T, c<sup>2</sup> estimates were 0.39 (0.14) and 0.22 (0.12). Conclusion: There are strong familial correlations in postmenopausal SHBG, IGF-I, and to a lesser extent T, which are consistent with a genetic etiology. For E<sub>2</sub>, and to a lesser extent T, correlations are consistent with substantial nongenetic familial factors. The latter might include maternal effects. Copyright © 2009 by The Endocrine Society. |
