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| Human Growth in Sickness and in Health |
Homeobox genes in vertebrate development
E.Boncinelli
A number of gene families have been identified in the past 20 years which play a role in the control of the development of the body, and in particular of the central nervous system, of vertebrates. Many of these genes are homeobox genes. Homeobox genes are regulatory genes characterised by the presence of a specific, evolutionarily conserved, DNA sequence termed homeobox, able to code for a protein domain of some 60 amino acid residues, termed homeodomain. It is through the action of their homeodomain that the protein products of the homeobox genes, the homeoproteins, bind to the regulatory regions of specific genes and control their expression. The first homeobox genes were identified in the fruit fly, Drosophila melanogaster through the study of the genetic control of its body plan. Here a complex of eight homeobox genes, termed homeotic genes, control the identity of the various body regions along the anterior-posterior axis. In vertebrates 39 genes have been identified which are the true homologues of the Drosophila homeotic genes. They have been termed Hox genes and are located in four homologous chromosomal loci. They appear to play a role in the specification of body regions along the rostro-caudal body axis and provide positional cues for the developing neural tube and in particular for the rhombencephalon (the developing hindbrain) and spinal cord, from the branchial area to the tail, but are not involved in controlling the development of the head and of brain regions anterior to the hindbrain.
Conversely, other homeobox genes belonging to other families have been reported to play such a role. Among them, the four genes belonging to the Otx and Emx families occupy a particular position and show an extremely restricted expression domain. In particular, Otx2 appears to play a crucial role in the early establishment of the rostral brain; Otx1 and Otx2 cooperate to define the posterior boundary of midbrain; and Emx1 and Emx2 play a major role in the developing cerebral cortex, whose extension is determined by the Emx2 gene products. These results may be relevant for the deeper understanding of congenital defects and multifactorial disorders.
The handling of data on psychomotor development
H. Lejarraga
Development is the course of changes in motor-sensory behaviour, emotional response, intelligence, learning and language. From a Gessellian perspective, it can be studied as the sequence of events (milestones) over time, performed by children at different ages.
Thus, a milestone becomes the dependent variable to be handled in epidemiological studies, in which the age of its achievement in population groups is the information of interest. Unlike anthropometric data, developmental data are not quantitative variables nor do they allow repeated evaluations of the same indicator at different ages. In cross sectional studies, logistic regression using the model p (x) = 1 / [1 + e (-a-bx) ] is the method of choice for the estimation of central values and variability of the age of attainment of developmental milestones. The following steps are recommended: 1) to confirm the developmental character of the milestone. 2) to evaluate if the data fit the model. 3) to evaluate if age or a monotonous transformation of age such as ln(age) explains the phenomenon (changes in "p" with age). 4) goodness of fit tests may be used to evaluate the degree of adjustment of the data to the model, 5) centiles of age of attainment of the milestone can then be estimated, together with confidence intervals (CI), which will be strongly related to sample size. Longitudinal studies yield also additional information, for example, mean and individual variation of time elapsed between the achievement of two sequential milestones, and relationships among different milestones over time. Data can be obtained from trained parents at home, from health personnel in repeated visits to a clinical setting, etc. Here, parametric methods are more convenient but if the model is incorrectly chosen it may lead to drastically incorrect values. Failure time models (time - to event response variable) are recommended. An empirical check of the appropriateness of the models to the distribution of the data should be carried out.
There certainly are other avenues of study of development. According to Piaget´s theory (genetic epistemology) the changing variable of development is the internal scheme constructed by the child for understanding the outside world, schemes that evolve through series of progressive stages. For Watson and behaviourism, development is progression of the learned behaviour, and it can be manipulated by changing the environment. Freud built a child theory from the interaction with adults; this theory has a chronological component (oral, anal, genital stages) and a non - chronological component (I, super I and the Id). Finally, we have the cultureless, those researchers who consider development as cultural (ecological) adaptation, a question of context. This type of information cannot be reduced to quantitative terms only. Instead, I recommend learn more on qualitative research, more familiar to the social sciences. Development is a place where biology, psychology and sociology meet, and for its study, in addition to the analytic logic we are used to apply in our everyday work, we should appeal to hermeneutics, a discipline using holistic logic. It will significantly help us, not only to have more information on development, but also to make it meaningful.
The contribution of auxology to the study of the aetiology of diseases
R.J. Rona
A scientist glancing through classical books of auxology will be puzzled by the almost total absence of chapters exploring the possible role of anthropometric measurements such as height in the causality of diseases. The thesis of this paper is that auxologists would be unwise to ignore this fundamental area of research. The presentation will review current knowledge on the possible effect of height on the mortality of cardiovascular diseases, respiratory illness and cancer, paying attention to the strengths and weaknesses of the evidence. The lecturer will discuss possible avenues for further progress in this area of research and the interrelation between auxology and other disciplines such as nutrition, endocrinology, and genetics. He will also explore emerging evidence on the association between body mass index and asthma as another area of great scientific activity in which auxological methods have been useful. This topic of research attracted scientific interest not more than seven years ago and already there are a large body of literature. This illustrates the need for auxologists to become aware of scientific development at an early stage. Thus if auxologists want to remain relevant they need to greatly increase their contacts with other disciplines and be aware of new topics of research.
Child Growth and Urbanism
L. Schell
It is common today to see little difference in child growth patterns between urban and rural populations. Today there is more heterogeneity in both urban and rural places. They overlap in function and structure, and the descriptions of urban rural differences once found in every textbook on human growth now are obsolete. That does not mean however that urban environments are as healthy for children as rural ones. Cities are characterized by steep social hierarchies that affect both the use of health care and children’s exposure to features that are not conducive to health. Identification of these features involves combining child growth examinations with careful measures of specific features of children’s environments. Already this approach has shown us that many pollutants have the ability, even at low levels, to affect physiological systems (e.g., the nervous, immune, endocrine and reproductive systems). This paper focuses on growth differentials within industrialized countries and shows the joint and separate effects of socioeconomic hierarchies and the pollutants that are the typical features of many urban places.
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