Difference in plasma bilirubin concentration between monozygotic and dizygotic newborn twins

Aim: To investigate whether inherited factors, other than those already known, influence the bilirubin concentration in neonates of northern European descent, by comparison of monozygotic and dizygotic twins with respect to differences in the plasma bilirubin concentrations between the twins. Methods: 77 healthy pairs of twins of the same gender with a gestational age ≥250 d and of northern European descent were included. Fourth postnatal day blood sampling was done. A multiple linear regression analysis was carried out with the difference in serum bilirubin concentration between the twins as the independent factor, and zygosity, gender, gestational age, postnatal age, maternal smoking, ABO blood-type incompatibility, and the differences between the twins in blood haemoglobin concentration, formula feeding and weight loss as dependent factors. Results: 27 pairs of twins were monozygotic and 50 pairs dizygotic. The analysis showed that the difference in serum bilirubin concentration between the twins was dependent on whether the twins were monozygotic or dizygotic, i.e. the estimated difference in serum bilirubin concentration between the monozygotic twins was 17.8 μmol l^-1 [SE 6.6 μmol l^-1, p = 0.02, 95% confidence interval (95% CI) 3.4, 32.3 μmol l^-1] less than the difference between the dizygotic twins, adjusted for the above-mentioned potential confounders. The difference in serum bilirubin concentration between the twins was positively correlated to the difference in weight loss (%) between the twins (adjusted estimate 5.2 μmol l^-1, SE 2.1 μmol l^-1, p = 0.01, 95% CI 1.2, 9.3 μmol l^-1).

Conclusion: In a population of northern European descent, other genetic factors than gender and ABO blood type were significant for the plasma bilirubin concentration in healthy infants.