Fact Sheet No 209
HUMAN GENETICS AND NONCOMMUNICABLE DISEASES
The last 20 years have seen an explosion of knowledge about the role genes play in health from the moment of conception to the day people die. It is now universally acknowledged that DNA determines not only the congenital malformations that kill millions of children, but also predisposes people to mental illness and major noncommunicable diseases (NCDs) such as cancer, cardiovascular disease, hypertension, asthma, diabetes and rheumatoid arthritis.
Single-gene defects, genetic predisposition and congenital malformations together form a large group of genetically determined conditions.
Single-gene defects, such as cystic fibrosis, haemoglobin disorders and haemophilia, are an important cause of fatal or chronically disabling diseases, especially in childhood. More than 9,000 single-gene conditions have now been identified. They occur worldwide, although some are more common in certain ethnic groups or geographic areas. Their incidence may be affected by differing demographic and cultural factors, such as maternal age or the prevalence of cousin marriages, for example.
Haemoglobin disorders -- conditions that involve errors in the production of oxygen-carrying haemoglobin in the blood -- are a striking example of the magnitude of single-gene defects.
Genetic predisposition is determined by the individual's genetic make-up, which contributes to susceptibility or resistance to disease. The picture is made further complex, involving an interaction of environmental factors.
Congenital malformations (CMs): There is an estimated 3 million infants annually, who are born with major CMs. Most of them die in the first three years of life.
Burden of Genetic Disorders: Single-gene defects have catastrophic effects on babies and children and place enormous emotional, practical and financial burdens on families. Diseases linked to genetic predisposition are equally devastating. Not only do they kill prematurely, but result in the long years of ill health and disability. Such chronic conditions are often compounded by the loss of work and income, possible poverty, loneliness and depression.
The burden of genetic disorders also falls on the health services of every country. Already today, diabetes mellitus, which affects at least 140 million people worldwide, with many of these cases genetically predisposed, alone accounts on average for 8% of total health budgets in industrialized countries. By 2025, WHO projects a more than twofold increase -- up to 300 million -- in the number of people with diabetes worldwide.
Promises and Pitfalls:Human genetics has enormous potential to achieve better health for all and to halt the advance of NCDs. It can provide us with the ability to give more accurate lifestyle advice, to screen, to diagnose and to counsel. Genetics has now advanced to the point where there are genetic tests for a number of conditions. In many cases, these can be carried out prenatally.
Among the new techniques will be gene therapy - the introduction of a gene sequence into a cell with the aim of modifying the cell's behaviour - perhaps to correct a genetic mutation (as in cystic fibrosis), to destroy a cell (as for cancer) or to modify susceptibility (as for coronary artery disease). Early trials of gene therapy are already underway.
Already controversies rage over issues such as the ethics of patenting genes or whether cloning should ever be permitted. Human dignity and well being remains at the centre of the many basic ethical, legal and social issues involved in the development of human genetics:
International Response: Human genetics is increasingly becoming the focus for massive investment from governments, research groups, biotech companies, aid organizations and medical charities worldwide. Among the international projects launched in this area, the Human Genome Project deserves special attention.
The Role of WHO is three-fold: The Organization initiates international
cooperation to develop genetic approaches to disease prevention and control in such areas
as hereditary diseases, those with genetic predisposition and congenital malformations.
Through international expertise and technical advice WHO also supports its Member States
in their efforts to plan and manage national genetic programmes. In doing so, WHO
advocates and promotes the following governing principles:
Partnerships: The work of WHO in the field of human genetics is supported by a wide network of international nongovernmental organizations, collaborating centres and research programmes, including the Thalassaemia International Federation, the World Federation of Hemophilia, the International Cystic Fibrosis Association, the International Clearinghouse for Birth Defects Monitoring Systems, etc. In all, WHO cooperates with various partners in more 80 both developed and developing countries.
Present and Future: Current trends in genetic approaches to disease prevention and control are strongly linked with the progress of international human genome research. Based on these trends, it is estimated that:
Now : It is possible to reduce the effect on mortality, disability and reproductive fitness in just under a third of single gene disorders. About 50% congenital abnormalities, 10% of inherited diseases and 2% of chromosomal disorders can be treated or corrected.
Within five years: Genetic approaches will become integral in many aspects of medical practice and it will be important for most health workers to have a basic understanding of medical genetics.
There will be further developments in genetic counselling, based on a family-oriented approach, neonatal screening and individual testing. The number of common diseases, including cancer, diabetes, heart disease and auto-immune disorders being treated in clinical trials of gene therapy will increase.
Within 20 years: All human genes will have been mapped and identified. The genetic mechanisms of each disorder will have been described. Medicine will become more predictive and preventive and diagnosis and therapy will become more specific and effective. Genetic diagnosis and counselling will be integrated into an increasing range of medical services. Genetic methodology will become a basic approach for health improvement and disease control. Gene therapy will be a universal method for disease prevention and treatment.
For further information, journalists can contact:
WHO Press Spokesperson and Coordinator, Spokesperson's Office,
WHO HQ, Geneva, Switzerland / Tel +41 22 791 4458/2599 / Fax +41 22 791 4858 / e-Mail: email@example.com