科研之友
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摘要
This present article deals with the question of how meaningful statistical risk assessments in genetic counseling may be for the decision-making process of individuals who ask for genetic advice. Even in some Mendelian diseases and generally in the case of multifactorial diseases it is not satisfactory to provide an a priori risk for all affected families. The question of whether a given person or his or her future children may develop the disease in question with severe, possibly untreatable symptoms may largely depend on individual circumstances. Accordingly, the inclusion of such circumstances in the assessment of an individual's a posteriori risk may largely deviate upwards or downwards from this a priori risk. Currently, the lack of such data often prevents the quantification of an individual a posteriori risk; it is, however, obvious that individual risk assessment will play an increasing role in future genetic counseling. Besides a better understanding of individual environmental influences our growing insight into the impact of epigenetic changes will enforce a re-evaluation of individual risks. Epigenetic changes acquired during fetal development or early childhood may lead to lasting physiological changes and, accordingly, may significantly affect the risk of an individual to develop a certain disease during his or her later life. Due to the complexity of genetic and epigenetic networks it is as inappropriate to categorize mutated genes or alleles which increase the risk for a certain disease as "bad" or "sick" genes as it is to consider genes with apparently health-promoting properties as "good" or "healthy" genes. Such rhetoric may foster feelings of either guilt or superiority in individuals and may have an even more politically dangerous impact by encouraging neo-eugenic thinking. In contrast, the goal of non-directive genetic counseling is to provide individuals seeking advice with reliable information which helps them arrive at a personal decision. Given their personal circumstances this decision should be ethically acceptable and realistically allow them to cope with their problem in their future lives. As seen in cases of Mendelian diseases, such as sickle cell anemia or thalassemias, heterozygous carriers may have selective advantages, in this particular case a natural resistance against Malaria tropica. This example demonstrates that a genetic burden may not have only disadvantages but also advantages for the health of a whole population. This consideration may hold for many alleles which have been present in the gene pool of a population for many generations, although they contribute to a genetic predisposition for a multifactorial disease. In debates about the heritability of a given trait, the heritability coefficient has often been used as an argument for and against the predominant impact of genes on the trait in question. The authors wish to remind their readers that this coefficient reflects the genetic variation measured in a given population divided by the variation of all possible parameters which affect the phenotypic trait. It neither gives an answer about the absolute influence of genes and other factors on this trait nor does it provide information about how unforeseen changes in the environment may affect the heritability of the trait in the future. Contrary to a common misunderstanding in public discussion this coefficient does not allow any conclusion on the interaction of genetic, epigenetic and environmental factors involved in the development of the trait in question in an individual.
Finally, i the closing section the authors highlight the opportunities of risk-adapted disease prevention.
- 出版日期2011-9
