Environmental rather than genetic factors determine the variation in the age of the infancy to childhood transition: a twins study.

OBJECTIVE: Using a twins study, we sought to assess the contribution of genetic against environmental factor as they affect the age at transition from infancy to childhood (ICT). STUDY DESIGN: The subjects were 56 pairs of monozygotic twins, 106 pairs of dizygotic twins, and 106 pairs of regular siblings (SBs), for a total of 536 children. Their ICT was determined, and a variance component analysis was implemented to estimate components of the familial variance, with simultaneous adjustment for potential covariates. RESULTS: We found substantial contribution of the common environment shared by all types of SBs that explained 27.7% of the total variance in ICT, whereas the common twin environment explained 9.2% of the variance, gestational age 3.5%, and birth weight 1.8%. In addition, 8.7% was attributable to sex difference, but we found no detectable contribution of genetic factors to inter-individual variation in ICT age. CONCLUSIONS: Developmental plasticity impacts much of human growth. Here we show that of the ∼50% of the variance provided to adult height by the ICT, 42.2% is attributable to adaptive cues represented by shared twin and SB environment, with no detectable genetic involvement.

Morbidity of overweight (>or=85th percentile) in the first 2 years of life.

OBJECTIVES: Our hypothesis was that morbidity related to overweight/obesity is already evident in infants and young toddlers. The major objectives of this study were (1) to assess the prevalence of overweight in a sample of hospitalized infants and (2) to assess the prevalence of morbidity in overweight infants in a community-based sample. METHODS: The hospital admission study population included 2139 infants, or=85th weight-for-height percentile in >or=2 measurements, >or=3 months apart), or=95th percentile had more admissions than expected, as well as a larger number of repeated admissions. In the second part of the study, we found that rates of developmental delays (mainly delayed gross motor skills) and snoring were significantly higher in infants of >or=85th percentile. In addition, although the results were not statistically significant, infants with overweight suffered more frequently from breathing problems, such as asthma and stridor. When the mothers were asked to assess whether their child was overweight, only 31.6% of mothers of overweight children thought that the child was overweight. CONCLUSIONS: The high admission rates for infants of >or=95th percentile and the high incidence rates of respiratory morbidity, snoring, and delayed gross motor skills in overweight infants support our hypothesis regarding early morbidity associated with overweight.