NZSM Online

Get TurboNote+ desktop sticky notes

Interclue makes your browsing smarter, faster, more informative

SciTech Daily Review

Webcentre Ltd: Web solutions, Smart software, Quality graphics

Feature

Two-Edged Sword of Genetics

Human genetics confronts us with important ethical and social issues.

Neville Honey

Suppose one of your parents has an incurable genetic disease. The symptoms started in his or her mid-forties and will lead to death after 15-20 years of mental deterioration. You have a 50% chance of having the disease yourself. There is now available a test for that disease, but should you take the test?

Suppose that you take the test and find that you do have the genetic defect. Each of your children has a 50% chance of inheriting the defect. Should you have children? If you (or your partner) become pregnant, the test can be done on the foetus. If the foetus also has the genetic defect, the child will develop the deadly disease, but only after decades of normal life. Should the pregnancy be terminated?

The disorder is Huntington's disease. Several families in New Zealand and many others overseas already face the dilemmas just described. The DNA test now allows us to diagnose the genetic defect, but leaves us with the issue of what we do with this knowledge. This is just one of many issues in human genetics.

Most genetic disorders are relatively rare in the general population, but as there are thousands of different disorders, the total incidence is high. A third of all paediatric admissions to hospital are related to genetic disorders, and about 2% of all people will be directly affected by a single gene defect at some stage in their lifetime.

Genetic disorders are highly variable in their effects. They range from the very severe, affecting both physical and mental development, to the inconsequential that do not fit the category of medical condition or illness. Many disorders are lethal at an early age, while others allow a good or normal life span. The age of onset can vary from infancy to middle-age.

Prenatal diagnosis is used for the identification and abortion of foetuses with genetic disorders. Is the abortion of such foetuses acceptable and, if so, which disorders are sufficient grounds for termination of pregnancy? The parents and families of children with severe genetic disorders are also adversely affected by the disorder. Is the effect on their lives a valid factor in the consideration of abortion? Couples with a child suffering from a severe genetic disorder are often not prepared to accept the risk of having a second similarly affected child, even if this means having no more children.

Genes and Behaviour

What is the role of genetics in the patterns of human behaviour? This question strikes at the core of our sense of identity and it raises issues of nature versus nurture. Is our behaviour predetermined or a consequence of our free will? Is our IQ the result of how we are brought up or something that is determined from birth? The evidence is that both genetic and environmental factors are important. There has been controversy in the US over whether differences in average IQ between racial groups are due to genetic differences. The advocates of genetic differences appear to ignore the contributions of environmental differences between the racial groups.

Another aspect of human behaviour is homosexuality. Is it inborn, or a consequence of the environment during upbringing, or a matter of choice? There is evidence that there is a significant genetic component to homosexuality. A recent report indicates that a proportion of male homosexuality shows patterns of inheritance that are consistent with X-linked inheritance [Gay Genetics, April]. If a prenatal test for homosexuality should ever become available, would this test be used for selective abortion?

What if genes predisposing to violent or criminal behaviour should be discovered and characterised? There are already suggestions that these behavioural traits may have a genetic component. Will preventative measures be taken, involving counselling, education, and careful attention to the environment, to prevent the expression of the socially unacceptable behaviour? Or will the response of others to those at risk induce the undesired behaviour? Will the names of at-risk people go onto police computers for monitoring as potential troublemakers?

Gene Therapy and Eugenics

Gene therapy is the correction of a genetic defect by the insertion of the functional gene in the appropriate cells of the patient. If the new gene is inserted into germ-line cells or into fertilised eggs, all of the cells of the person would be corrected. However, this genetic alteration would be in the person's germ-line cells and so passed down to any descendants. Somatic cell gene therapy inserts the functioning gene only into the selected tissues where the new gene is expected to have a positive benefit. There are considerable technical difficulties, but the inserted gene will not be inherited by any children. Gene therapy is not currently performed in New Zealand, but may in the future when it becomes a standard medical procedure.

Is somatic cell therapy the ethical equivalent of organ transplants? It is currently an expensive treatment with limited applications, so is the money better spent on other aspects of health care? With somatic cell therapy the genetic defect continues to be passed down to successive generations. Germ line therapy could overcome this limitation, but introduces a permanent change to the human gene pool. Should we deliberately alter the human gene pool, with unknown consequences?

Eugenics proposes the improvement of the human gene pool by reducing the incidence of undesirable genes and increasing the incidence of desirable genes. Many early proponents of eugenics assumed that there was a "superior" social class or race, which just happened to be their own. Eugenics was discredited when it was used to justify actions aimed at those seen as being genetically inferior. But are there arguments for eugenics on a more rational basis? The prevention of genetic disorders through either carrier screening or prenatal diagnosis is a form of eugenics. Is this a desirable action? Is the increased spread of desirable traits a worthwhile goal? Do we have the knowledge to judge what constitutes an improvement and who would decide what is desirable or undesirable?

Future Shock, or a Brave New World?

The human genome project aims to generate the complete human gene sequence. This project is expected to be a valuable tool for the study and understanding of human genetics. How far will this new knowledge extend? What will be the implications for society if we could eventually identify all the genes and their functions? Could we ultimately generate a complete genetic profile of every person (at least in wealthy societies), specifying his or her strengths and weaknesses? Such profiles might be used to direct our educational and employment opportunealistic, although, given the amazing progress of the past few years, it would be foolish to make firm predictions about what the limits are going to be in the future. We do not yet know what the limits to the capabilities of DNA technology will be.

As our understanding of human genetics increases, it will have an increasing impact on people and society and will therefore confront us with the issue of how to deal with that knowledge. The science of human genetics can be regarded as a two-edged sword. It has the potential to be an invaluable tool for improving human well-being, but it also has the potential for misuse. There needs to be continued debate on the issues of human genetics, so that there is a general understanding of the issues and their implications, and to decide what is acceptable to society.

Dr Neville Honey is a lecturer in genetics at Massey University.