Salivary Diurnal Glucocorticoid Profiles in Monozygotic Twins with Intratwin Birthweight Differences.

Context: Low birthweight (bw) and unfavorable intrauterine conditions have been associated with metabolic sequelae in later life, but little is known about their impact on glucocorticoid metabolism. Objective: We studied monozygotic twins with intratwin bw differences to analyze the long-term impact of bw on glucocorticoid metabolism. Methods: 46 monozygotic twin pairs with bw differences of <1 SDS (concordant; n = 29) and >= 1 SDS (discordant; n = 17) were recruited. At 6.9 years (mean age), saliva samples were collected (at 7 hours, 13 hours, 18 hours and 21 hour) and analyzed with liquid chromatography-tandem mass spectrometry (LC-MS/MS). Results: We found significant or highly significant intratwin correlations in all twin pairs at 3 of 4 (cortisol), and 4 of 4 (cortisone) time points. Graphic evaluation of the diurnal cortisol patterns for each twin pair showed a distinct alignment in all groups. Analyses of the change of intratwin differences over the day by mixed linear modeling showed no intratwin differences in diurnal patterns. Regression analyses of intratwin differences at 7:00 hours showed a significant influence of catch-up growth, indicating lower cortisol concentrations in smaller twins with more catch-up growth (adj. R-2 = 0.159, P =.014, beta = -3.71, F(1,42) = 9.15, f(2) = 0.19). Conclusion: In monozygotic twins with intratwin bw differences, intratwin catch-up growth showed a moderate influence on intratwin differences in morning cortisol concentrations. We observed no differences regarding diurnal patterns. In contrast, in all groups, we found significant intratwin correlations for cortisol and cortisone over the day and a pronounced graphic alignment of cortisol diurnal patterns. We therefore suggest a predominant significance of the genetic background compared with bw differences on cortisol metabolism.