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 newborn survival and respiratory health and are determined by complex interactions between genes and the environment. However, the contribution of genetic dominance has been scarcely investigated. We aimed to investigate the genetic and environmental influences on infant weight, length, and head circumference in singleton and twin infants at birth and four months of life, using both traditional and behavioral genetics approaches accounting for genetic dominance. A total of 173 newborns (65 singletons and 54 twin pairs) were consecutively recruited within the HEALS and earlyFOOD projects. At birth and four months of life, developmental outcomes were expressed as standard deviation scores (z-scores), and information about maternal and family factors was collected using questionnaires. We first considered singletons and a randomly selected twin for each pair and run linear regression models at birth and four months of life for each outcome. Then, we considered the twin pairs and estimated behavioral genetic 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 outcomes at birth (p < 0.05) and fertility treatment was significantly associated with higher birth length (? = 0.58, p = 0.026). ACDE models highlighted significant percentages of variance explained by additive genetic factors (23 to 29%). Significant percentages of variance explained by shared environmental factors were observed 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 dominance genetic factors was observed for length at birth (37%, p = 0.037). The joint assessment of additive and non-additive genetic effects, together with shared and unique environmental influences, provides new insights into the study of the determinants of respiratory-related developmental outcomes such as infant weight, length, and head circumference.