ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: Front. Endocrinol. 2020 11:142. doi: 10.3389/fendo.2020.00142

• A delayed transition from the infancy to the childhood growth stage contributes to sub-optimal growth outcomes.• Using a novel method to assess the timing of infancy-childhood transition (quantification of patterns of adjacent monthly weight-for-age z-score (WAZ) deviation correlations), this transition was found to take place at the age of 12 months in UK. The authors in this study find that the transition takes place earlier in rural Gambia (9 months).• The authors hypothesize that while a later transition allows maximal extension of the high rates of growth during the infancy, an earlier transition may negatively affect the growth outcomes in childhood but also offers an extended window for later catch-up.

This article is to some extent complementary to the article by German et al. discussed above. The model of Karlberg on which this article is based defines the infant-childhood transition as the period during which the rapid infantile growth decreases towards the more stable state and growth rate plateau of childhood. It is postulated to be associated to a progressive shift from the leading role of insulin and the insulin-like growth factors as mediators of nutritional status in the fetus to the role of the endogenous regulation of growth hormone. At that time, the child enters his/her defined percentile of growth. To assess the timing of this shift, the authors examine the change in the month-to-month correlation of the weight for age Z scores (WAZ). The shift in the correlations between adjacent WAZ from positive to negative values is associated with a change from infantile to childhood growth. Because of the importance of early growth for the development of long-term complications in the child, understanding the variation and factors in the timing of transition could be very useful if some of the factors could be modified to positively affect growth. In two UK studies, this shift was found to take place around the age of 12 months. Surprisingly, in the present study, applying the same modeling as the UK studies, the transition in rural Gambia was found to take place earlier, at 9 months. Assuming that the technical limitations of this complicated model do not affect the interpretation of the results, why would the transition from infancy to childhood take place earlier in Gambia compared to UK? It may reflect a trade-off: when energetic resources are limited and are prioritized for immediate, life-saving tasks (such as fighting infections), rapid growth takes a back seat to ensure that the remaining resources can still support key tasks such as brain development. Catch-up growth may take place later is energetic resources are again plentiful. From a philosophical point of view, it may be that ponderal (and therefore linear) growth should not take place at the detriment of higher functions.