The central developmental task of middle child-hood is to learn as much as possible about the world and one's place in it. Children absorb vast quantities of information during these years, gleaned from a variety of sources including their families, their peers, the greater community and their own independent exploration. Among the more formal settings for facilitating many children's learning is the school classroom. Here, children have an opportunity to devote their full attention to mastering those basic skills of reading, writing and arithmetic necessary to continue learning across a lifetime. For some children, mastering these basic skills may require extraordinary effort. Approximately 5% of the children in public schools in the United States (US) are identified as having some type of learning disability . Since this behaviour is the efferent expression of brain activity, it is presumed that these learning disabilities are related to some form of neuroanatomic, neurophysiologic or neurochemical pathophysiology. However, it is not yet well understood how the brains of children with learning disabilities differ from those of other children or how such differences may be related to observed differences in behaviour.
The term learning disability (LD) traditionally refers to unexpected underachievement in adequate educational settings, i.e. that academic achievement of children and adults with LD typically is not commensurate with some estimate of their "ability" [1, 2]. Most definitions of LD have at least three other elements in common: i) heterogeneity; ii) neurobiologic or other intrinsic factors; and iii) not caused primarily by cultural, educational, environmental and socio-economic factors, or by other disabilities (mental deficiency, visual or hearing impairments, or emotional disturbance) [1-4]. Thus, LD is not a single disability but a special education category composed of disabilities in one or more domains of academic achievement (see Table I for the current US federal definition of LD and attending eligibility criteria) .
Competence in young children is defined not only by the acquisition of culturally and age appropriate specific cognitive abilities, but also by the acquisition of intrapersonal characteristics and interpersonal skills that aid the child in meeting major developmental goals and in dealing with challenges from the environment. A variety of influences have been documented as necessary for the development of competence in healthy young children growing up in relatively advantaged circumstances. These influences include genetic contributions, physical maturation, characteristics of the family, preschool and school environments, the nature of the child's peer group, neighbourhood and family social support networks, as well as higher order influences such as family social class and culture. These specific biological and psychosocial influences do not operate independently but rather are linked to each other, so that the contributions of one influence depend upon the nature and contributions of other influences.
Learning problems represent a major health concern throughout the world. As we enter the 21st century, never have so many children around the world had opportunities for healthy development and eventual productivity, and never have so many children suffered from physical insults leading to learning disabilities and subsequent lack of opportunities. The reason for this paradox relates to demographics, increasing survival from some infectious diseases that lead to brain injury, increasing numbers of disasters and an unacceptable high rate of undernutrition. The numbers of children in the world increase daily, infant mortality is decreasing and there are more poor people than ever before.
We have commented in previous issues of the Annales on the health benefits that are anticipated because of the remarkable advances in human genomics. Perhaps, in highlighting these advances, we unintentionally led some to conclude that the "nature vs nurture" debate, i.e. whether health and other outcomes are determined predominantly by our genetic endowment or environments, has been resolved. If winners are to be declared in this debate, it is likely to go to those who argue that it is folly to ignore either one. The answer most likely lies not only in "nature" or only in "nurture" but in their interactions. Health professionals markedly influence many aspects of the interplay between these two aspects of daily living. We should not let the bright prospects of "genetic engineering" blind us to the highly significant "phenotypic engineering" we engage in daily.