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1 December 2007 Resemblance for Age at Menarche in Female Twins Reared Apart and Together
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Menarche is a significant developmental event in the lives of young females. Genetic and family environmental influences on the timing of its occurrence are explored in the first formal analysis using reared-apart and reared-together monozygotic (MZA, MZT) and dizygotic (DZA, DZT) twin pairs. Mean age at menarche was 12.50 years (SD = 1.67) for the reared-apart pairs and 12.86 years (SD = 1.49) for the reared-together pairs. Intraclass correlations for age at menarche were 0.56 for MZA twins, 0.16 for DZA twins, 0.70 for MZT twins, and 0.41 for DZT twins. The mean within-pair difference was 1.07 years (SD = 1.04) for MZA twins, 1.67 years (SD = 1.59) for DZA twins, 0.64 year (SD = 0.86) for MZT twins, and 1.43 years (SD = 1.34) for DZT twins. These results are consistent with genetic influence, although the lower correlations for reared-apart twins and their larger within-pair differences suggest that age at menarche is partly affected by common rearing environments. Feeling understood by one's father during the growing-up years was significantly associated with earlier age at menarche, and a comparable trend was found for feeling understood by one's mother. These findings are considered with reference to current theories of pubertal timing.

Nancy L. Segal and Joanne Hoven Stohs "Resemblance for Age at Menarche in Female Twins Reared Apart and Together," Human Biology 79(6), 623-635, (1 December 2007).
Received: 18 December 2006; Accepted: 1 July 2007; Published: 1 December 2007

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