Genetic and environmental components of neonatal weight gain in preterm infants.

BACKGROUND AND OBJECTIVES Postnatal nutrition and subsequent weight gain or failure in the neonatal period are likely regulated by both the environment and the genetic background. With the goal of estimating the variability of postnatal weight gain due to genes and environment, comparison between monozygotic (ie, genetically identical) and dizygotic (genetically similar as 2 siblings) twins can be performed. METHODS This study selected a very homogenous set of monozygotic and dizygotic twins who met the following inclusion criteria: gestational age between 30 and 36 weeks, birth weight between 1250 and 2200 g, and length of stay >12 days. Opposite-gender pairs and pairs that differed >20% in terms of birth weight were excluded from this analysis. The outcome measure of this study was the daily weight gain expressed in grams per kilogram per day during the period between day of birth and day of discharge. The average difference between members of a pair was computed in the 2 groups of twins, and heritability was estimated. RESULTS The within-pair differences of the outcome measure were lower for monozygotic twins than for dizygotic twins, suggesting a strong genetic component. The total variance of the phenotype under study is explained by 2 sources of variation, additive genetic (87% [95% confidence interval: 67% to 94%]) and unique environment (13% [95% confidence interval: 6% to 33%]) components. CONCLUSIONS This high heritability estimate could suggest using this set of criteria to identify genes that regulate postnatal weight gain or failure.