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When is molecular genetic testing for colorectal cancer indicated?

The genetic mutations causing many of the syndromes which confer a high inherited risk of colorectal cancer have now been identified. These include familial adenomatous polyposis, hereditary non-polyposis colorectal cancer, Peutz-Jeghers syndrome, Cowden's syndrome and juvenile polyposis. In all these diseases, the precise mutation is nearly always unique to a particular family; there are few mutation hot spots. This means that mutation detection is technically demanding. Nonetheless, genetic testing can now be used clinically to confirm the diagnosis in affected individuals, and to predict whether an "at risk" family member has inherited the disease and should therefore have endoscopic screening. Because current technology does not detect all mutations, a negative result in a definitely affected individual is diagnostically unhelpful and does not allow predictive testing of other family members. When a mutation can be detected, it is diagnostically very useful, and allows better management of all family members.

Adenomatous Polyposis Coli↗

X-ray-induced specific-locus mutations in the ad-3 region of two-component heterokaryons of Neurospora crassa. II. More extensive genetic tests reveal an unexpectedly high frequency of multiple-locus mutations.

More extensive genetic tests have been performed on a series of 832 X-ray-induced specific-locus mutations in the ad-3 region of a 2-component heterokaryon (H-12) of Neurospora crassa, reported earlier (Webber and de Serres 1965). Using new tester strains and techniques for performing large-scale genetic tests (heterokaryon, dikaryon and trikaryon) to characterize ad-3 mutants induced in 2-component heterokaryons, new data have been obtained on this sample of X-ray-induced ad-3 mutants. These new data show that unexpectedly high frequencies of both single-locus (gene/point) mutations and multilocus deletions in the ad-3 region have additional, but separate, sites of recessive lethal (RLCL) damage in the immediately adjacent genetic regions. The frequencies of these X-ray-induced multiple-locus mutants in the ad-3 region are orders of magnitude higher than expected on the basis of target theory and classical models of chromosome structure during interphase. Current models of interphase chromosome structure in higher eukaryotes as revealed by chromosome "painting" offer a possible explanation of the Neurospora data.

Adenine↗

The law's response to reproductive genetic testing: questioning assumptions about choice, causation and control.

The law's response to reproductive genetic testing depends on a number of assumptions about choice, causation and control which need to be questioned. From the preconception stage forward, the illusion of choice may raise such fundamental questions as the woman's choice not to be tested, limits on genetic information, and the availability of reproductive options. In turn, assumptions about choice raise questions about the responsibility for results and the connection between choice and causation in the context of wrongful birth and life actions. Assumptions made about control over reproductive choice and over causing 'harm', will impact on the development of future law.

Abortion, Eugenic↗

Genetic testing, life insurance, and adverse selection.

Life insurance is a key element of the UK social structure in terms of family protection and house purchase; it thus needs to be viewed in this broad context, rather than solely as a commercial activity. Insurers have not so far actively requested genetic tests for life insurance, but have insisted on knowing of and being able to act on existing genetic test information. The main reason given for this has been to avoid serious adverse selection; however, this has never been adequately estimated. Review of the different major categories of Mendelian genetic disorders suggests that the scope for adverse selection is extremely limited and that insurers would lose little, and possibly gain more, by foregoing the disclosure and use of this information in relation to life insurance policies of 'normal' size and nature. The likely future use in service of genetic tests based on susceptibility or population screening makes it especially important that the issue is rapidly resolved for Mendelian disorders; so far there is no sign that insurers are willing to achieve this.

Eligibility Determination↗

Use of nucleic acid probes in genetic tests.

Advances in molecular genetics have led to the development of clinical assays for several genetic diseases. Two general testing approaches are available: direct detection of the genetic mutation or indirect detection using DNA markers close to, or within, the defective gene. Direct testing at the nucleic acid level is available for diseases in which the basic defect is well characterized, such as sickle cell anemia. Several methods are available for detection of the point mutation that causes sickle cell anemia including: routine Southern blot analysis, allele specific oligonucleotides, and polymerase chain reaction gene amplification. For diseases such as cystic fibrosis, in which the basic genetic defect has not yet been characterized, an indirect approach is used. This approach relies on linkage analysis using DNA markers close to the genetic defect. Inheritance of the DNA marker is followed through the family. Unlike direct testing, the DNA marker does not detect the actual genetic defect. Therefore, a prediction of inheritance of the linked disease is given based on the risk of recombination between the disease locus and the DNA marker. An appreciation of the differences between the direct and indirect approaches is necessary to understand their attributes and their limitations.

Base Sequence↗

Incidence and mutation rates of Huntington's disease in Spain: experience of 9 years of direct genetic testing.

BACKGROUND: Prior to the discovery of the Huntington's disease (HD) mutation, the prevalence, incidence, and new mutation rates for this disease were based on the presence of progressive choreic movements and a positive family history. OBJECTIVE: To evaluate the uptake of the HD genetic analysis in Spain, and to provide additional information on the epidemiology of this disease from the experience of 9 years of direct genetic testing. METHODS: From 1994 to 2002, CAG repeat length was determined in 317 patients with symptoms compatible with HD. In all cases, demographic, clinical, and family data were carefully reviewed. RESULTS: HD diagnosis (CAG repeat length >/=36) was confirmed in 166 (52%) symptomatic cases. Of these, 76 (45.8%) reported a positive family history and in 21 cases (12.7%) family history was negative. New mutation events were genetically proven in three families and highly suspected in another, estimating that the minimum new mutation rate for HD in our population is >4%, with a potential mutation rate of 8%. More than 16% of all HD cases had late onset (>59 years) of symptoms, and in three quarters of these the family history was negative. The incidence rate for the autonomous communities of Navarra and the Basque country, based on the number of newly diagnosed cases by genetic testing, was 4.7 per million per year. CONCLUSIONS: Direct HD genetic testing shows that the incidence and mutation rates of the disease are 2-3 times higher than previously reported. We also demonstrated the relevance of CAG repeat length assessment in diagnosing patients with late onset of symptoms and negative family history for HD.

Adolescent↗

Attitudes toward genetic testing and fetal diagnosis, 1990-1996.

With few exceptions, existing research on attitudes toward genetic testing and prenatal diagnosis is based on small studies using nonprobability samples of specialized populations. In this paper, we use a nationally representative sample from the General Social Survey to report on attitudinal change between 1990 and 1996, and to explore socio-demographic predictors of public views on genetic technology and reproduction in the context of changing mass media coverage between 1988 and 1995. During that period, media coverage of prenatal testing became both less frequent and less favorable, despite increasing use of this technology, whereas media reports about other types of genetic testing increased in frequency and became more favorable. Between 1990 and 1996, attitudes toward genetic testing remained stable, although the attitudes of specific demographic subgroups may be changing in different directions. Attitudes toward abortion in case of genetic defect became more negative over the period studied. We explore some of the implications of these findings.

Abortion, Induced↗

The diffusion of new genetic tests for predicting disease.

This paper examines the pathways by which new genetic tests will become available to the public. In view of the scarcity of genetic specialists, the pathway is likely to involve primary care physicians. Other pathways entail state-mandated testing, community-based programs, or testing by laboratories without much involvement of primary care physicians. When testing does become available the "destination" will be either family-centered testing or population-oriented screening. The deterrent to screening will not be the inability to detect disease-causing mutations but the costs and attitudes of providers and the public. When tests are provided primarily to provide information about risks to future children, some people will oppose screening on religious or moral grounds. When there are no inexpensive treatments, some will fear that insurance companies and employers will use tests to deny them health care coverage. Some may not want to know their risks for disorders about which little can be done. For common, multifactorial disorders, genetic tests will have low predictive value. Because of these problems, the decision to be tested, regardless of the destination, requires that "testees" be fully informed and consent to testing. When acceptance rates are low, screening is less likely to be cost-effective; family-centered testing becomes the default destination.

Genetic Diseases, Inborn↗

Genetic counseling issues in predictive genetic testing for familial adult-onset neurologic diseases.

Genetic counseling is important in any genetic testing situation in order to address the various issues related to obtaining a genetic diagnosis. Presymptomatic testing for adult-onset neurodegenerative disease, in particular, presents a complex counseling scenario. It is imperative to discuss the potential impact of test results on patients' family dynamics, insurability and employability, family planning, and future health in addition to ascertaining a complete understanding of recurrence, inheritance, and testing parameters. The Huntington disease presymptomatic testing protocol is well-defined and has been used for more than 10 years. These guidelines, which protect both patient and provider, can now be applied to other diseases as further presymptomatic testing capabilities are realized.

Adult↗

Predictive genetic testing in young people: when is it appropriate?

Predictive genetic testing is currently offered to adults for a range of conditions, even when there is no possibility of prophylaxis or treatment. However, similar testing in children and adolescents is advised against in international guidelines. Despite this, several authors have argued against the existing guidelines. Given the lack of empirical evidence, it is important that clinicians are aware not only of the guidelines, but also of the arguments in favour of such testing.

Adolescent↗

Genetic testing for inherited breast and ovarian cancer syndromes: important concepts for the primary care physician.

The remarkable advances in the area of genetic testing are transforming the way clinical medicine is practised. In the case of the inherited breast-ovarian cancer syndrome the ability to engage in genetic testing of BRCA genes has raised novel issues over caring for patients who are at increased risk for these malignancies. The primary care physician is likely to play a pivotal role in identifying such persons. As only 10-15% of all breast cancers are caused by directly heritable mutations, cultivating the ability to identify those who may be at increased risk is an important skill for the primary care physician. Once it is established that an individual is at risk of BRCA mutation, the physician must understand the potential benefits and drawbacks of the various genetic BRCA tests. Taking such factors into account leads to the development of an appropriate plan for evaluation. Careful attention must also be paid to social and psychological issues that may affect patients and their families.

BRCA2 Protein↗

Ethical issues of genetic testing and their implications in epidemiologic studies.

PURPOSE: To discuss and summarize the ethical controversies related to genetic testing and screening, and their effects on the research and other professional activities of epidemiologists. METHODS: We reviewed the literature and proposed legislation to discuss the controversies related to the ethical issues of genetic testing in epidemiologic research. RESULTS: From a review of the literature and proposed legislation, we found these controversies may continue for some time and will probably add to the duties and difficulties of epidemiologists. It is important for the profession to respond to developments such as the proposed federal Genetic Confidentiality and Nondiscrimination Act of 1996 (Senate Bill 1898), which is summarized here; changes in research protocols and informed-consent forms as well as inclusion of other professionals from many disciplines will be necessary. In addition to revising training, and expanding their ethical code, epidemiologists should respond to public concerns about genetic information by disseminating knowledge about freedom to conduct clinical research, protection of the individual, and the limits of genetic information. CONCLUSIONS: The possibility of genetic discrimination may complicate epidemiological research unless the public, employers, insurers, physicians, and researchers reach a consensus on the meaning of, and need for, genetic information. Although ethical concerns are appropriate, they will make accrual of study subjects and tissue samples more difficult.

Epidemiology↗

Predictors of uptake of obesity genetic testing among affected adults.

Given that a large number of candidate genes coding for a tendency toward obesity have been identified and some findings have been replicated, we explored characteristics of those who would be most likely to obtain future genetic testing for this tendency. During a series of focus groups, obese respondents rated their likelihood of obtaining testing under conditions in which either genetically-targeted drug treatment would be available, a positive test would be associated with a prognosis for developing diabetes, or neither of these. Interest in testing was greater given the first two scenarios than the third. Older age and belief that genetics were an important cause of obesity were associated with greater interest. For the first two scenarios, higher educational status was associated with greater interest, while for the third, respondents who said emotional issues caused overweight and those who crash-dieted intermittently were more likely to want genetic testing. Although further research is required to validate these findings, this study is the first published report of respondents' ratings of likelihood to obtain genetic testing for propensity to obesity, and suggests strong interest in genetic testing among some people, even in the absence of further treatment implications of the test.

Adult↗

Factors influencing uptake of genetic testing for colorectal cancer risk in an Australian Jewish population.

There is a significant excess of colorectal cancer in the Australian Ashkenazi Jewish community. This excess can partially be attributed to inherited factors that are over represented in this population, such as the APC variant I1307K, which is associated with a modest increase in colorectal cancer risk. There is currently only sporadic clinical genetic testing offered for this variant, as neither the exact increase in cancer risk and therefore the appropriate screening strategies for I1307K carriers, nor the acceptability of such testing in Jewish communities have been determined. This study reports a high acceptability of such genetic testing within a community sample of 300 Australian Jewish individuals--94% of participants would have a test for predisposition to colorectal cancer and a majority would make this decision based on the desire for information for their families and to decrease their own cancer risk. Some concerns were noted about genetic testing for cancer predisposition, including insurance discrimination, test accuracy and confidentiality.

Australia↗

Genetic testing in pheochromocytoma- and paraganglioma-associated syndromes.

Genetic understanding of pheochromocytoma (PHEO) and paraganglioma (PGL) syndromes has recently expanded with the identification of the involvement of the mitochondrial complex II peptides, namely the succinate dehydrogenase subunit B (SDHB), subunit C (SDHC), and subunit D (SDHD). In patients with PHEO and/or PGL genetic testing for germline mutations in SDHD and SDHB has been recommended, in addition to the PHEO susceptibility genes VHL and RET. After careful clinical assessment of the patient, suspected familial disease may direct the clinician to the appropriate gene for testing. In the absence of obvious features of familial disease, the decision regarding the appropriate gene for testing is more difficult. Such testing can be costly and time consuming, but a rational prioritization of gene testing can streamline the process. Therefore in order to achieve this for apparently sporadic cases we propose a decision matrix based on site of tumor, functionality, and age at presentation.

Adrenal Gland Neoplasms↗

Genetic testing and quality control in diagnostic laboratories.

To evaluate the quality of genetic testing for cystic fibrosis, 136, 145 and 159 laboratories participated in a European study in 1996, 1997 and 1998, respectively. We sent six purified DNA samples carrying the more common CFTR mutations with the request to test them using routine protocols. A panel of experts reviewed the results together with the raw data.

Cystic Fibrosis↗