growth velocity during puberty. The lack of association in early infancy could be explained by the fact that height growth is not yet dependent on growth hormone at that age [14]. Also, we found a possible biological explanation for the interaction (p = 0.045) for the SNP in HHIP (Hedgehog interacting protein), suggesting an effect on PHV in infancy but not in puberty. HHIP is a component of the hedgehog signal transduction pathway involved in embryogenesis and development [21]. This pathway influences the transcription of many target genes and is important for development of many tissues and organs. It is important in early embryogenesis and cell proliferation, including limb and central nervous system development [21],[22]. Therefore it seems plausible that variants in HHIP would only play a role in early infancy but not in puberty. However, since the HHIP interaction does not appear to be very strong in our data, this result needs replication.
