Genetic and environmental influences on infant anthropometry at birth and four months of life: evidence from singleton and twin data in the HEALS and earlyFOOD projects

Prenatal and postnatal developmental outcomes are associated with newbornsurvival and respiratory health and are determined by complex interactions betweengenes and the environment. However, the contribution of genetic dominancehas been scarcely investigated. We aimed to investigate the genetic andenvironmental influences on infant weight, length, and head circumference insingleton and twin infants at birth and four months of life, using both traditionaland behavioral genetics approaches accounting for genetic dominance.A total of 173 newborns (65 singletons and 54 twin pairs) were consecutivelyrecruited within the HEALS and earlyFOOD projects. At birth and four monthsof life, developmental outcomes were expressed as standard deviation scores(z-scores), and information about maternal and family factors was collected usingquestionnaires. We first considered singletons and a randomly selected twinfor each pair and run linear regression models at birth and four months of lifefor each outcome. Then, we considered the twin pairs and estimated behavioralgenetic models to disentangle the contribution of additive genetic effects (A),genetic dominance (D), shared (C) and unique (E) environmental influences.In regression analyses, twin births were significantly associated with lower outcomesat birth (p < 0.05) and fertility treatment was significantly associated withhigher birth length (? = 0.58, p = 0.026). ACDE models highlighted significantpercentages of variance explained by additive genetic factors (23 to 29%). Significantpercentages of variance explained by shared environmental factors wereobserved at four months of life for weight (43%, p = 0.029) and head circumference(50%, p = 0.004). A significant percentage of variance explained by dominancegenetic factors was observed for length at birth (37%, p = 0.037). The joint assessment of additive and non-additive genetic effects, together withshared and unique environmental influences, provides new insights into thestudy of the determinants of respiratory-related developmental outcomes suchas infant weight, length, and head circumference.