Similarities and Differences in Diurnal Salivary Adrenal Hormones in Monozygotic Twins with Discordant Birthweight

Introduction: Dehydroepiandrosterone sulphate is increased in formerly small-for-gestational age singletons and in smaller twins compared to their normal-weight co-twin. Less is known concerning other adrenal hormones. We compared diurnal salivary profiles in monozygotic twins with intra-twin birthweight (bw) differences to analyse the long-term impact of bw and persistent intra-twin auxological differences on various adrenal hormones.

Methods: Forty-six monozygotic pre-pubertal twin pairs with bw difference of <1 standard deviation score (SDS) (concordant; n = 29, 13 female) and ≥1 SDS (discordant; n = 17, 6 female) were recruited. At a mean age of 6.9 years, saliva samples were collected (7:00 a.m./waking, 1:00 p.m., 6:00 p.m., and 9:00 p.m.) and analysed with liquid chromatography-tandem mass spectrometry.

Results: Diurnal salivary concentrations showed significant intra-twin correlations in all twin pairs for nearly all time points: progesterone and androstenedione (4/4 time points), 17-hydroxyprogesterone (2/4). However, in the discordant group, mean progesterone differed significantly (p = 0.018) between the smaller (3.27 nmol/L, SD 3.87) and the larger twin (0.72 nmol/L, SD 0.42) at 7:00 a.m., and intra-twin differences were observed at 3/4 time points. Regression analyses of intra-twin differences confirmed that actual hormonal parameters were explained mainly by the co-twin parameter. However, at 6:00 p.m., progesterone concentration of the smaller twin was explained by bw (Β -1.102; SE 0.563; p = 0.05) and actual weight (Β 0.799; SE 0.327; p = 0.019).

Conclusion: The significant correlations within monozygotic twin pairs in all measured hormones at nearly all time points suggest a strong genetic influence on the adrenal axis. Among the discordant twin pairs, we found significant variations in progesterone, suggesting additional long-lasting influence from intrauterine conditions on adrenal hormones with possible metabolic consequences.