title: Environmental rather than genetic factors determine the variation in the age of the infancy to childhood transition: a twins study.
abstract: 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).
  
  
  METHODS
  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.
authors.affiliation: Department of Pediatrics, Bnai Zion Medical Center, Haifa, Israel. Electronic address: alinagerman@gmail.com.
authors.forename: Alina
authors.initials: A
authors.lastname: German
authors.affiliation: Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Gregory
authors.initials: G
authors.lastname: Livshits
authors.affiliation: Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, NY.
authors.forename: Inga
authors.initials: I
authors.lastname: Peter
authors.affiliation: Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Ida
authors.initials: I
authors.lastname: Malkin
authors.affiliation: Haifa District Health Office, Ministry of Health, School of Public Health, Haifa University, Haifa, Israel.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Dubnov
authors.affiliation: Haifa District Health Office, Ministry of Health, Haifa, Israel.
authors.forename: Hannah
authors.initials: H
authors.lastname: Akons
authors.affiliation: The Lorry I. Lokey Interdisciplinary Center for Life Sciences and Engineering, Technion - Israel Institute of Technology, Haifa, Israel.
authors.forename: Michael
authors.initials: M
authors.lastname: Shmoish
authors.affiliation: Rappaport Faculty of Medicine, Technion - Israel Institute of Technology, Haifa, Israel.
authors.forename: Ze'ev
authors.initials: Z
authors.lastname: Hochberg
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology*; D002657:Child Development; D004777:Environment; D005260:Female; D005500:Follow-Up Studies; D005865:Gestational Age; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D017584:Reproductive History; D012189:Retrospective Studies; D012737:Sex Factors; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*