with advanced maternal age. However, the committee was concerned about the use of prenatal diagnosis for identification of trivial characteristics or conditions. It was the consensus of this committee that prenatal diagnosis should only be offered for the diagnosis of genetic disorders and birth defects. A family history of a diagnosable genetic disorder warrants the offering of prenatal diagnosis, regardless of maternal age, as does determination of carrier status in both parents of an autosomal recessive disorder for which prenatal diagnosis is available. Prenatal diagnostic services for detection of genetic disease for which there is a family history should be reimbursed by insurers (see Chapters 2 and 7). Ability to pay should not restrict appropriate access to prenatal diagnosis or termination of pregnancy of an affected fetus.

The committee felt strongly that the use of fetal diagnosis for determination of fetal sex and the subsequent use of abortion for the purpose of preferential selection of the sex of the fetus represents a misuse of genetic services that is inappropriate and should be discouraged by health professionals. More broadly, reproductive genetic services should not be used to pursue eugenic goals, but should be aimed at increasing individual control over reproductive options. As a consequence, additional research is needed on the impact of prenatal diagnosis, particularly its immediate and long-term impact on women, and on the design and evaluation of genetic counseling techniques for prenatal diagnosis for the future.

Testing for Late-Onset Disorders

Science is moving closer to defining the genetics of such adult disorders as Alzheimer disease, a variety of cancers, heart disease, and arthritis, to name a few (see Chapter 2). A combination of genetic and environmental factors plays a predominant role in most people afflicted with these disorders, but we do not yet understand why some people with a certain gene(s) develop a disease and others do not. Although further work may eventually elucidate the gene(s) involved, there may be long delays until the time when effective interventions are available for many disorders. Furthermore, not all affected individuals will have an identifiable genetic basis to their disorder. Thus, the complexities involved in determining and establishing susceptibility, sorting out potential environmental influences, and devising a strategy for counseling and treatment will pose tremendous challenges in the future.

Many of these diseases do not manifest clinically until adulthood and may become apparent only in middle age or later. Predictive or presymptomatic testing and screening can provide clues about genetic susceptibility or predisposition to genetic disorders. For monogenic disorders of late onset, such as Huntington disease, tests will usually be highly predictive. Many common diseases usually have multifactorial—or complex—causation, including both multiple genetic factors and environmental effects; for these disorders, prediction will be less certain.



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