遗传检测综述

目前,遗传检测正在更多的国家、更广泛的范围内被采用。然而,在中国人们还不大熟悉遗传检测的原理、类型、技术、对社会的益处以及国内或国际是如何对它进行管理的。随着遗传检测的广泛使用,正确的监督显得相当必要。对近年来遗传检测所取得的进展进行了粗略的回顾,这将帮助我们对人类遗传学和分子医学革命的新时代有更多的了解。     

Medical errors related to inappropriate genetic testing in liver transplant patients

Genetic testing of genes that encode proteins expressed by liver hepatocytes (clotting factors, alpha 1-antitrypsin, cytochrome P450 enzymes) is common in clinical practice. These tests use DNA extracted from peripheral blood lymphocytes (PBL) and are based on the assumption that PBL DNA can be used as a surrogate for hepatocyte DNA. However, in individuals who have undergone liver transplantation, hepatocyte DNA is that of the donor while PBL DNA remains that of the recipient. It follows that in liver transplant patients, genetic testing of the recipient's PBL DNA does not provide accurate results for proteins expressed by donor hepatocytes. Therefore, genetic testing of clotting factors, alpha 1-1-antitrypsin, cytochrome P450 enzymes, and other proteins expressed by hepatocytes is unreliable and inappropriate in liver transplant patients (inappropriate genetic testing). A review of the records of 215 consecutive liver transplant patients at our institution identified: one medical error and one near-miss medical error related to inappropriate genetic testing, 14 cases of inappropriate genetic testing, and 21 unnecessary duplicate genetic testing requests. We recommend laboratories performing genetic testing create systems to prevent inappropriate and duplicate genetic testing and that physicians be cognizant of the appropriate indications for genetic testing in liver transplant patients.     

Genetic testing for disease susceptibilities: consequences for genetic counseling

The role of genetic counseling in future testing for inherited susceptibilities for common diseases is debated. Currently, genetic testing, ideally supported by genetic counseling, is most often used to modify the assessment of genetic risk of Mendelian-inherited disease in high-risk individuals for the purpose of personal decision-making. By contrast, it is anticipated that genetic testing will be used to identify increased disease susceptibility in low-risk individuals for the purpose of instituting medical or lifestyle interventions to modify risk for future disease.     

Calculation of the morbid risk in genetic-epidemiologic studies of age-dependent diseases

Distributions of age at onset are widely used in the genetic epidemiology of age-dependent diseases. Examples are estimation of recurrent risks in genetic counselling and testing genetic hypotheses in segregation and linkage analyses. In this study, morbidity parameters are defined, including age-specific morbidity rates, morbidity net risk (incidence), and cumulative incidence (population risk, an integrated measure of population susceptibility to the disease at the moment of the study). Age-specific morbidity risks are calculated from the respective morbidity rates, which are analogous to mortality rates used in demography. Population data typically used for calculation of morbidity rates are discussed. Methods of calculation of morbidity rates based on the data of single and interval epidemiological studies are described. Methods for calculating standard errors of these parameters, estimating their statistical reliability, and testing statistical hypotheses are discussed.     

Genetic testing and risk assessment for spinal muscular atrophy (SMA)

Spinal muscular atrophy (SMA) is one of the most common autosomal recessive diseases, affecting approximately 1 in 10,000 live births, and with a carrier frequency of approximately 1 in 50. Because of gene deletion or conversion, SMN1 exon 7 is homozygously absent in approximately 94% of patients with clinically typical SMA. Approximately 30 small intragenic SMN1 mutations have also been described. These mutations are present in many of the approximately 6% of SMA patients who do not lack both copies of SMN1, whereas SMA of other patients without a homozygous absence of SMN1 is unrelated to SMN1. A commonly used polymerase chain reaction/restriction fragment length polymorphism (PCR-RFLP) assay can be used to detect a homozygous absence of SMN1 exon 7. SMN gene dosage analyses, which can determine the copy numbers of SMN1 and SMN2 (an SMN1 homolog and a modifier for SMA), have been developed for SMA carrier testing and to confirm that SMN1 is heterozygously absent in symptomatic individuals who do not lack both copies of SMN1. In conjunction with SMN gene dosage analysis, linkage analysis remains an important component of SMA genetic testing in certain circumstances. Genetic risk assessment is an essential and integral component of SMA genetic testing and impacts genetic counseling both before and after genetic testing is performed. Comprehensive SMA genetic testing, comprising PCR-RFLP assay, SMN gene dosage analysis, and linkage analysis, combined with appropriate genetic risk assessment and genetic counseling, offers the most complete evaluation of SMA patients and their families at this time. New technologies, such as haploid analysis techniques, may be widely available in the future.     

Attitudes toward genetic testing in patients at risk for HNPCC/FAP and the German population

Adequate knowledge regarding hereditary diseases and genetics, as well as personal attitudes toward gene tests, are major determinants of optimal utilization of genetic testing. In the present study, we aimed to explore the general attitudes toward genetic testing in a sample representative of the German general population (n = 2,076) and to compare the attitudes of persons at risk for hereditary non-polyposis colorectal cancer/familial adenomatous polyposis (HNPCC/FAP) (n = 36) who had attended a university genetic counseling service, with a matched general population sample. We administered a subset of a questionnaire previously used in a Finnish study (Jallinoja et al., 1998). The 12 statements pertain to approval, disapproval, and concern for genetic testing. Overall, the results reveal high approval of genetic testing in the German population and in at-risk persons. In accordance with other studies, we find that the attitudes of individuals for whom hereditary disease is a salient issue of personal relevance and the attitudes of the general public are very similar. Only a few significant differences between these two samples emerged, indicating that at-risk persons hold a more favourable view of the testing. One intriguing finding was the high rate of "don't know" responses, especially in the general population sample. Compared to results from Finland, approval of genetic testing is lower in the German population, and endorsement of "don't knows" is remarkably higher. We argue for increased attention to the issue of attitude change after genetic counseling and for the need of comparative cross-cultural research on attitudes toward gene technology.     

Molecular Genetic Testing in Endocrinology—A Practical Guide

ObjectiveTo discuss the factors to consider when evaluating patients with a suspected genetic endocrine disorder, so as to guide practicing endocrinologists through the process of genetic testing and result interpretation.MethodsThe author’s experience and review of appropriate literature have been used to give a personal perspective on the role of genetic testing in hereditary endocrine disorders.ResultsRecent advances in our understanding of genetics and genomics have uncovered that they have a far more important role in the pathogenesis of endocrine disease than previously appreciated. Not only are we expanding our understanding of rare mendelian disorders such as multiple endocrine neoplasia type 1 and 2, but we are also beginning to understand the clinical significance of genetic factors in the pathogenesis of common disorders such as obesity and dyslipidemia.ConclusionsIt can be difficult to appreciate the clinical significance and utility of genetic testing that is currently available, and the interpretation of genetic test results can be challenging. Decisions on whether genetic testing is needed should be made on a case-by-case basis, with the endocrinologist and geneticist working together from the outset. (Endocr Pract. 2012;18:85-89)     

A Regression Modeling Approach for Describing Patterns of HIV Genetic Variation

We introduce a novel approach for describing patterns of HIV genetic variation using regression modeling techniques. Parameters are defined for describing genetic variation within and between viral populations by generalizing Simpson's index of diversity. Regression models are specified for these variation parameters and the generalized estimating equation framework is used for estimating both the regression parameters and their corresponding variances. Conditions are described under which the usual asymptotic approximations to the distribution of the estimators are met. This approach provides a formal statistical framework for testing hypotheses regarding the changing patterns of HIV genetic variation over time within an infected patient. The application of these methods for testing biologically relevant hypotheses concerning HIV genetic variation is demonstrated in an example using sequence data from a subset of patients from the Multicenter AIDS Cohort Study.     

How Distinctive is Genetic Information?

There is extensive discussion of the ethical, social, economic and political issues associated with the use of technologies based on DNA techniques. Many of these debates are premised on the assumption that DNA, and the genetic information that may be derived from it, have unique features which raise new social and ethical issues. In this paper it is argued that several of the features associated with DNA which are sometimes regarded as unique are shared with other biological materials. Others owe more to the cultural image of DNA and some of the metaphors used to discuss it in biology and in wider debates than to the biological properties of DNA. The paper discusses the concepts of genetic material and genetic information and the social construction of DNA in relation to forensic DNA databases, paternity testing and genetic testing for disease. The paper concludes by suggesting that there are seven areas where issues related to DNA and genetic information are at least relatively distinct.     

Parental attitudes toward genetic testing for pediatric deafness

Recent molecular genetic advances have resulted in genetic testing becoming an option for deaf individuals and their families. However, there is little information about the interest in such testing. To investigate this issue, parents with normal hearing who have one or more deaf children were surveyed about their attitudes toward diagnostic, carrier, and prenatal genetic testing for deafness. This population was chosen because it represents the majority of individuals who are encountered in clinical practice, given that 90%-95% of deaf individuals are born to persons with normal hearing. Of 328 surveys distributed, 96 were completed and returned. Of the respondents, 96% recorded a positive attitude toward genetic testing for deafness, including prenatal testing, although none would use this information to terminate an affected pregnancy. All respondents had a poor understanding of genetics, with 98% both incorrectly estimating the recurrence risk of deafness and misunderstanding the concept of inheritance. Notably, these findings were similar in the group who had had genetic testing for their children and in the group who had not, suggesting either that the parents who received genetic testing did not receive genetic counseling or that the counseling was not effective. On the basis of these results, it was concluded that this population is interested in the use of genetic testing and that testing should not be done without first providing formal genetic counseling. Appropriate counseling can help parents to understand the risks, benefits, and limitations of genetic testing.     

Sequence alterations can mask each other's presence during screening with SSCP or heteroduplex analysis: BRCA genes as examples

For mutation detection, various screening techniques are widely used because DNA sequencing, the gold-standard method, is still considered to be expensive and laborious for high-throughput screening. Single-strand conformation polymorphism (SSCP) analysis, heteroduplex analysis (HA) and their variant techniques are popular and frequently used for this purpose. It is widely accepted that when searching for unknown sequence variations, any revealed distinct pattern should always be sequenced. We give examples here of the BRCA1 and BRCA2 genes where the SSCP/HA techniques can produce ambiguous predictions if used to detect known genetic variants compared to positive controls. Using direct DNA sequencing, we provide evidence that in such cases, mutations or polymorphisms can mask each other's presence. This phenomenon can often influence the results of any DNA testing because genetic variations such as single-nucleotide polymorphisms occur frequently in the human genome. We suggest that even in the case of known electrophoretic patterns of well-characterized genetic alterations, every sequence alteration should be confirmed by direct DNA sequencing, especially if genetic testing is carried out for diagnostic purposes.     

Actuarial considerations on genetic testing.

In the UK the majority of life insurers employ relatively liberal underwriting standards so that people can easily gain access to life assurance cover. Up to 95% of applicants are accepted at standard terms. If genetic testing becomes widespread then the buying habits of the public may change. Proportionately more people with a predisposition to major types of disease may take life assurance cover while people with no predisposition may take proportionately less. A model is used to show the possible effect. However, the time-scales are long and the mortality of assured people is steadily improving. The change in buying habits may result in the rate of improvement slowing down. In the whole population, the improvement in mortality is likely to continue and could improve faster if widespread genetic testing results in earlier diagnosis and treatment. Life insurers would not call for genetic tests and need not see the results of previous tests except for very large sums assured. In the UK, life insurers are unlikely to change their underwriting standards, and are extremely unlikely to bring in basic premium rating systems that give discounts on the premium or penalty points according to peoples genetic profile. The implications of widespread genetic testing on medical insurance and some health insurance covers may be more extreme.     

Impact of BRCA1 testing on women with cancer: a pilot study

We sought to understand better the impact of genetic testing and counseling in a group of women who had early breast cancer (age <50) or ovarian cancer and a family history of cancer. Thirty-five women underwent genetic counseling and genetic testing for BRCA1/2 at the University of Colorado Cancer Center, Hereditary Cancer Clinic. Psychological assessment (IES and Hopkins Symptom Checklist) was made before counseling, and 1 month after genetic test results were reported to women. A statistically significant decrease in anxiety was evidenced 1 month after results were given (p = 0.024). Decreased intrusive thoughts related to genetic testing were seen only for those testing negative (p = 0.0003). Women diagnosed with cancer less than 1 year prior to genetic testing experienced the greatest cancer-specific distress (p = 0.01) and distress related to genetic testing (p = not significant). Satisfaction with the counseling and testing process was high. In conclusion, genetic testing and counseling can occur with little anxiety and stress. However, women less than 1 year from a cancer diagnosis will experience the greatest distress associated with genetic testing and counseling. Women who are considering genetic testing and counseling close to a diagnosis of cancer may require greater psychological support.     

Genetic model selection in two-phase analysis for case-control association studies

The Cochran-Armitage trend test (CATT) is well suited for testing association between a marker and a disease in case-control studies. When the underlying genetic model for the disease is known, the CATT optimal for the genetic model is used. For complex diseases, however, the genetic models of the true disease loci are unknown. In this situation, robust tests are preferable. We propose a two-phase analysis with model selection for the case-control design. In the first phase, we use the difference of Hardy-Weinberg disequilibrium coefficients between the cases and the controls for model selection. Then, an optimal CATT corresponding to the selected model is used for testing association. The correlation of the statistics used for selection and the test for association is derived to adjust the two-phase analysis with control of the Type-I error rate. The simulation studies show that this new approach has greater efficiency robustness than the existing methods.     

Controlling futures? Online Genetic Testing and Neurodegenerative Disease

Online personalized genetic testing services offer accessible and convenient options for satisfying personal curiosity about health and obtaining answers about one’s genetic provenance. They are especially attractive to healthy people who wish to learn about their future risk of disease, as Paul Mason’s (2017) case study of “Jordan” illustrates. In this response, we consider how online genetic testing services are used by people diagnosed with a common neurodegenerative disease, Parkinson’s disease, to gain a sense of certainty regarding the future.     

Gender differences in attitudes among those at risk for Huntington's disease

This report presents and discusses selected findings regarding gender differences from an Australian-based study that investigated attitudes of individuals at risk for Huntington's disease (HD) towards genetic risk and predictive testing. Clear gender differences emerged regarding perceived coping capacity with regard to predictive testing, as well as disclosure of the genetic risk for HD to others. Female participants were more likely to disclose their genetic risk to others, including their medical practitioners, while male participants were three times more fearful of disclosing their genetic risk to others. These findings are of interest in light of gender differences that have consistently been reported regarding the uptake of predictive testing for HD, other genetic conditions, and health services more generally. While gender differences cannot provide a fully explanatory framework for differential uptake of predictive genetic testing, men and women may experience and respond differently to the genetic risk for HD and possibly other inherited disorders. The meanings of genetic risk to men and women warrants further exploration, given anticipated increases in genetic testing for more common conditions, especially if post-test interventions are possible. These issues are also relevant within the context of individuals' concerns about the potential for discrimination on the basis of genetic risk or genetic test information.     

Beyond consent: ethical and social issues in genetic testing

Informed consent is a vital ethical doctrine in clinical medicine and, through genetic counselling, is being applied to genetic testing. But genetic testing raises issues that transcend the traditional concept of informed consent. Genetic tests are adopted without demonstrable clinical benefit, and the consequences of testing can reach beyond the individual to their families and communities. Understanding the social and cultural context of genetic testing will lead to more informed discussion and debate on these issues.     

Rates and outcomes of testing for lynch syndrome in a national colorectal cancer screening programme

BackgroundLynch Syndrome (LS), the most common cause of hereditary colorectal cancer (CRC), is characterised by pathogenic variants in mismatch repair (MMR) genes. Universal testing of all CRCs for LS can increase detection. Rates and outcomes of testing in Ireland’s national CRC screening programme have not been examined previously.MethodsCRCs diagnosed at two screening sites between 2015 and 2020 were identified. Patient records were used to determine if CRCs had been tested for MMR deficiency and if detected, what downstream testing to rule out LS or genetic testing to confirm LS was undertaken.ResultsOver five years, 206 CRCs were diagnosed. Testing for LS was carried out for 100% of CRCs at site A and 69% of CRCs at site B. Of CRCs tested for LS, 14 (8%) were MMR deficient. After downstream testing for BRAF mutation or hypermethylation of MLH1, three CRCs were identified as potentially LS-related. Of these two individuals declined genetic testing and one was lost to follow-up.ConclusionsBy 2020 both sites had implemented universal testing of all CRCs for LS. A small number of individuals were identified as being eligible for genetic testing for LS, however those offered declined testing and one individual was lost to follow up. This highlights the importance of universal testing and the need for referral pathways to ensure all appropriate individuals are referred onwards to genetic services.     

The present status of higher plant bioassays for the detection of environmental mutagens

Higher plants provide valuable genetic assay systems for screening and monitoring environmental pollutants. They are now recognized as excellent indicators of cytogenetic and mutagenic effects of environmental chemicals and are applicable for the detection of environmental mutagens both indoor and outdoor. Comparisons between plant and nonplant genetic assay systems indicate that higher plant genetic assays have a high sensitivity (i.e. few false negatives). Two assays which are considered ideal for in situ monitoring and testing of airborne and aqueous mutagenic agents are the Tradescantia stamen hair assay for mutations and the Tradescantia micronucleus assay for chromosome aberrations. Both assays can be used for in vivo and in vitro testing. Other higher plant gentoxicity assys which have a large number of genetic markers and/or data base and are also highly suitable for testing for genotoxic agents include Arabidopsis thaliana, Allium cepa, Hordeum vulgare, Vicia faba, and Zea mays. Since higher plant systems are now recognized as excellent indicators of the cytotoxic, cytogenetic, and mutagenic effects of environmental chemicals and have unique advantages for in situ monitoring and screening it is recommended that higher plant systems be accepted by regulatory authorities as an alternative first-tier assay system for the detection of possible genetic damage resulting from pollution or the use of environmental chemicals. The results from higher platn genetic assays could meke a significant contribution in protecting the public from agents that can cause mutation and cancer. The advantages possessed by higher plant genetic assays, which are inexpensive and easy to handle, make them ideal for use by scientists in developing countries.     

Testing of chemicals for mutagenic activity with Schizosaccharomyces pombe

Two genetic end-points are used for testing mutagens in Schizosaccharomyces pombe: forward mutations of the loci which encode steps early in the adenine synthetic pathway and reversion of certain selected mutants. 54 chemicals have been tested for at least one of the genetic end-points. The relevant literature has been reviewed through 1979.