Salivary diurnal glucocorticoid profiles in monozygotic twins with intra-twin birthweight-differences

Low birthweight (bw) and unfavourable intrauterine conditions have been associated with metabolic sequelae in later life, but little is known about their impact on glucocorticoid metabolism. We studied monozygotic twins with intra-twin bw-differences to analyse the long-term impact of bw on glucocorticoid metabolism.46 monozygotic twin-pairs with bw-differences of <1SDS (concordant; n = 29) and ≥1SDS (discordant; n = 17) were recruited. At 6.9 years (mean age), saliva samples were collected (at 7 h, 13 h, 18 h and 21 h) and analysed with liquid chromatography-tandem mass spectrometry (LC-MS/MS).We found significant or highly significant intra-twin correlations in all twin pairs at 3/4 (cortisol), respectively 4/4 (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 intra-twin differences over the day by mixed linear modelling showed no intra-twin differences in diurnal patterns. Regression analyses of intra-twin differences at 7:00 h showed a significant influence of catch-up growth, indicating lower cortisol concentrations in smaller twins with more catch-up growth (adj.R²=0.159, p = 0.014, ß=-3.71, F(1,42) = 9.15, f²=0.19).In monozygotic twins with intra-twin bw-differences, intra-twin catch-up growth showed a moderate influence on intra-twin differences in morning cortisol concentrations. We observed no differences regarding diurnal patterns. In contrast, in all groups, we found significant intra-twin 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.