Since it has been suggested by some studies in the medical literature that increased height is associated with higher IQ, one might think that rapid "catch up" growth after a period of nutrition restriction would lead to an improved outcome. A recent study suggests that just the opposite may be true (at least if you're a bird.).
This study was done in zebra finches, but there are other studies to suggest the same factors may be at play to some degree in humans [Morley 2004]. In the zebra finch study (abstract below, entire article freely accessible at PLoS Biology), chicks experienced a period of poor nutrition early in life, the after which they were provided a rich diet that allowed them to "catch up" to their siblings. The authors found that this rapid compensatory growth was associated with a detrimental cognitive outcome in the longterm. In fact, the chicks that did the most catching up with respect to growth had the poorest learning skills as adult birds.
How might this be relevant to PWS? Infants with PWS are hypotonic and weak feeders, and often a great deal of effort is needed to be sure that these babies take in enough nutrition and don't experience "failure to thrive". Growth hormone (GH) therapy has proven very beneficial for infants (and kids and adults) with PWS. Benefits include improved motor development, increased lean mass, decreased fat and as well as a suggestion of improved cognitive development (see previous blog). The current article raises the possibility that rapid growth after a period of poor nutrition may not be ideal. Obviously, there are considerable differences between zebra finches and humans, and there is less evidence of any long term problems in humans who experience significant "catch up" growth. Nevertheless, a reasonable take home message is that it is important to assure that infants with PWS receive adequate nutrition during their early development, so that the need for "catch up" growth is minimized. As previously suggested [Myers 2006], care must also be taken that once children with PWS start receiving GH, their caloric intake be appropriately increased to allow optimal growth and development. Finally, another reason to promote adequate early nutrition and reduce the need for catch up growth is provided by the finding that "catch up" growth is associated more "catch up fat", which leads to an increased risk of obesity and type II diabetes later in life [Dulloo 2006].
Fisher MO, Nager RG, Monaghan P.
Several studies have demonstrated that poor early nutrition, followed by growth compensation, can have negative consequences later in life. However, it remains unclear whether this is attributable to the nutritional deficit itself or a cost of compensatory growth. This distinction is important to our understanding both of the proximate and ultimate factors that shape growth trajectories and of how best to manage growth in our own and other species following low birth weight. We reared sibling pairs of zebra finches on different quality nutrition for the first 20 d of life only and examined their learning performance in adulthood. Final body size was not affected. However, the speed of learning a simple task in adulthood, which involved associating a screen colour with the presence of a food reward, was negatively related to the amount of growth compensation that had occurred. Learning speed was not related to the early diet itself or the amount of early growth depression. These results show that the level of compensatory growth that occurs following a period of poor nutrition is associated with long-term negative consequences for cognitive function and suggest that a growth-performance trade-off may determine optimal growth trajectories.
A press release about this article is available here.