Familial Correlations in Postmenopausal Serum Concentrations of Sex Steroid Hormones and Other Mitogens: A Twins and Sisters Study

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 (E2), 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 (h2) and nongenetic factors common to sisterships (c2) 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...