Population genetic screening programs

24.6 Population screening programs are established to offer individuals the opportunity to obtain more information about their current and future health. Armed with this information, they can make better-informed choices about health care, lifestyle and reproduction. The Health Council of the Netherlands has commented that population genetic screening programs seek ‘to enable people to achieve greater autonomy and to decide upon a course of action that is acceptable to them’.^[5]

24.7 Screening programs are an expanding aspect of health care. As the cost of genetic testing decreases and the range of available tests increases, it is likely that population genetic screening will become feasible for a greater number of conditions.^[6]

24.8 Screening can be undertaken in two ways:

• pro-active screening, where large populations are systematically targeted and offered screening tests; or

• opportunistic screening, where tests for an unsuspected disorder are offered by doctors when a person has sought medical advice for another reason.^[7]

24.9 Population genetic screening programs differ from each other in scope and objective, and these factors will determine which population is screened, the tests offered, and the time at which screening takes place. These factors will also determine the implications and possible uses of the information generated by the screening program. Most programs share three general aims: to decrease the prevalence of a disorder, to reduce the health effects of a disorder, and to inform individuals about their reproductive choices.

24.10 Population genetic screening can give individuals information about their health that they would not otherwise have sought, and this may motivate them to seek treatment or make lifestyle changes. By identifying illness that would otherwise have gone undiagnosed, or have been detected too late for effective treatment, genetic screening can improve individual health in some cases. Screening results can also inform individual reproductive decisions and, because choices may reduce the likelihood of children being born with certain genetic disorders, screening programs can decrease the incidence of these disorders in the population.

24.11 Population screening also has research value, enabling researchers to collect information about the prevalence and incidence of particular disorders in the community. Sometimes these research objectives overlap with objectives related to the health of individuals.^[8] An example, discussed below, is the current project for screening Jewish children in Sydney private schools for Tay-Sachs disease carrier status.

24.12 Population screening may be conducted on a large scale by offering tests to entire populations or to a sub-set of individuals within a population. Screening is directed either to the widest population that can be reached (mass screening) or to a defined group (selective screening).

Mass screening

24.13 Mass screening programs test entire populations or community groups in order to identify a condition or conditions suitable for treatment or prevention.^[9] Most participants will be asymptomatic and will be unaware that they might have a genetic disorder. Mass genetic screening is most appropriate for detecting treatable but often under-diagnosed conditions, and diseases such as cancer and heart disease where an individual’s risk can be reduced by monitoring, medication and lifestyle changes.^[10] Newborn screening programs are an example of mass genetic screening.

Selective screening

24.14 Genetic screening of large populations can be time-consuming and expensive. Selective genetic screening is a more economical method of detecting individuals who carry a genetic mutation. The screening of groups with a higher prevalence of the mutation is more likely to identify affected individuals than screening the general population. Fewer resources are therefore expended on screening people who are not affected.

24.15 Selective screening programs are directed at population sub-groups that are distinguishedby a common characteristic. Groups may be defined by:

• a higher risk of carrying a gene related to disease—for example, African populations have a relatively high prevalence of sickle cell anaemia;

• shared symptoms—for example, people with high cholesterol levels might be screened for genetic causes of familial hypercholesterolaemia, a disorder that causes elevated cholesterol levels and can contribute to the development of heart disease;

• phase of life—for example, newborn children or adolescents may be screened for certain genetic conditions; or

• workplace—for example, a company might screen all its employees for a genetic mutation that increases their risk of disease when working in a particular work environment.

24.16 Selective screening programs that target individuals who may be at increased risk for a genetic disorder often focus on community, racial or ethnic groups in which a disorder is more prevalent, or on individuals with a family history of an inherited disorder—for example, screening of families with a history of familial adenomatous polyposis, a form of colorectal cancer.

24.17 Cascade screening is a form of selective screening that seeks to identify and test relatives of people diagnosed with a genetic condition. Like other forms of selective screening, cascade screening is a more efficient and cost-effective method of identifying affected individuals than mass screening, and may be conducted through genetic registers. Genetic registers and family genetic information are discussed in Chapter 22.

24.18 Selected population groups defined by shared symptoms or disabilities that have a variety of causes may be screened to determine if, in some cases, the condition results from genetic causes. An example is the screening of individuals with learning disabilities to detect those with Fragile X syndrome, a genetic condition that causes mental retardation.^[11] Screening of high-risk families for Fragile X is conducted in all Australian States.^[12]

24.19 Screening programs can be targeted at populations at different stages of life: pre-implantation,^[13] prenatally,^[14] at birth, during early childhood or during adulthood. The stage at which screening is conducted has implications for issues of consent, counselling and the availability of treatment, which are discussed later in this chapter. For example, screening children for late-onset genetic disorders is generally regarded as unacceptable.^[15] Genetic screening of adolescents and adults is usually performed to identify carrier status or predict future disease. For example, the Tay-Sachs program discussed below screens adolescents for carrier status before they start families. Adult screening tests include haemochromatosis, breast cancer susceptibility and familial hypercholesterolaemia. In general, screening of adults and adolescents is recommended only for conditions that are reasonably treatable.^[16]

24.20 Populations exposed to particular work environments might also be suitable for screening. For example, individuals with a predisposition to sickle cell anaemia may be more likely to develop the condition if exposed to carbon monoxide or cyanide. An employer might screen to determine which employees are not suited to tasks where exposure to these substances may occur. The use of genetic screening and other genetic testing in employment is discussed in Part H. Other contexts where selective screening might be used include immigration, sport, and law enforcement. Genetic testing in these contexts is discussed elsewhere in this Report.^[17]