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Monozygotic Twins with Birth-Weight Differences: Metabolic Health Influenced more by Genetics or by Environment?

Background: Low birth-weight (bw), low birth-length (bl), unfavourable intrauterine conditions and post-natal catch-up growth can have an impact on growth and metabolic health later in life. Objective: We studied genetically identical twins with intra-twin bw-differences due to twin-twin transfusion syndrome from birth to adolescence and analysed the long-term impact of bw and catch-up growth on metabolic parameters. Subjects and Methods: Forty-three postpubertal monozygotic twin-pairs (mean age 17.4 years) were examined. Twenty-two pairs were discordant (intra-twin bw- and/or bl-difference ≥1 SDS) of which 12 (55%) experienced catch-up growth. Auxological parameters and blood pressure were measured, a fasting blood sample was collected and bio-impedance spectroscopy was carried out. Results: Irrespective of differences in birth parameters and postnatal catch-up growth, a significant intra-twin correlation was found for nearly all measured parameters of body composition (skinfold, waist-hip circumference, relative body fat/lean body mass) and metabolic health (total, and low-density lipoprotein-C/high-density lipoprotein-C, Apolipoprotein A and B, C-peptide). As an exception to this, and only for the former smaller twins who showed postnatal catch-up growth, a significantly higher fasting insulin level was found compared to that of the co-twins (mean insulin level: 8.4 vs. 5.7 µIU/mL; p < 0.01). Auxology remained different until adulthood: even in subjects with catch-up growth the former smaller twins were significantly lighter (mean-body mass index-SDS: –0.42 vs. 0.21; p < 0.05) and shorter (mean height-SDS: –0.07 vs. 0.37; p < 0.05) than their co-twins. Conclusion: In this special group of monozygotic twins with intra-twin bw-differences and catch-up growth, we found that the genetic background was a more important factor in determining later metabolic health than bw and/or catch-up growth.