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Psychological implications of advances in genetics--3 predictive testing.

The psychosocial effects of genetic testing on individuals and families are complex, and the implications should be considered carefully. Testing of children for carrier status or adult-onset conditions is not usually advised. Professionals need to be aware of the complexity of the issues affecting clients and provide appropriate education and support.

Adaptation, Psychological↗

Predictive testing for multiple endocrine neoplasia type 2A (MEN 2A) based on the detection of mutations in the RET protooncogene.

BACKGROUND: The identification of inherited mutations in the RET protooncogene (RET) associated with multiple endocrine neoplasia type 2A (MEN 2A) has enabled the development of a genetic test to identify asymptomatic carriers of disease. METHODS: Genomic DNA was extracted from 96 members of an MEN 2A kindred. The polymerase chain reaction was used to amplify the RET exon known to contain the associated mutation. The mutation results in a new restriction endonuclease site and is detected by digestion with the appropriate enzyme. Inheritance of the mutation was verified with a previously developed genetic linkage test. RESULTS: We found that (1) mutations vary among kindreds but are consistently inherited within kindreds, (2) invariable correlation exists between mutation and disease (43 mutations in 43 affected individuals), (3) determination of the genetic status by linkage-based testing was precluded by recombination events and the informativeness of genetic markers, and (4) mutation analysis presymptomatically identified two genetically affected individuals. CONCLUSIONS: Direct genetic analysis for mutations in RET circumvents the limitations of linkage-based genetic testing and current biochemical screening assays. This method will be the diagnostic test of choice for the identification of asymptomatic individuals at risk for MEN 2A.

Amino Acid Sequence↗

Working up policy: the use of specific disease exemplars in formulating general principles governing childhood genetic testing.

Non-therapeutic genetic testing in childhood presents a "myriad of ethical questions"; questions which are discussed and resolved in professional policy and position statements. In this paper we consider an underdiscussed but strongly influential feature of policy-making, the role of selective case and exemplar in the production of general recommendations. Our analysis, in the tradition of rhetoric and argumentation, examines the predominate use of three particular disease exemplar (Huntington's disease, Tay-Sachs disease and sickle cell disease) to argue for or against particular genetic tests (predictive testing and testing for carrier status). We discuss the influence these choices have on the type and strength of subsequent recommendations. We argue that there are lessons to be drawn about how genetic diseases are conceptualised and we caution against the geneticisation of medical policy making.

Child↗

Presymptomatic tests in Huntington's disease and dominant ataxias.

Huntington's disease (HD) and dominant ataxias (SCA) represent neurodegenerative hereditary diseases dominantly transmitted for which a direct and accurate genetic test is now available for molecular confirmation and presymptomatic test. Predictive testing programs, according to published international guidelines, are available worldwide. A large number of subjects (n=165) required a predictive HD diagnosis, although only 36% completed the program flow-chart and received the final genetic result (26 had a positive, 34 negative result for mutation). In 4 cases, an allele of intermediate range (33-34 CAGs) was found. Two of these shared the intermediate allele with an expanded repeat. In this case, we estimated the patient's risk to have affected children over the usually reported 50%. In 4 cases, the presymptomatic diagnosis was requested by persons at-risk for SCA1 and SCA3/Machado-Joseph disease. There were no adverse events to results of both HD and SCA presymptomatic diagnoses.

Age of Onset↗

Results of the National Institute of Allergy and Infectious Diseases Collaborative Clinical Trial to test the predictive value of skin testing with major and minor penicillin derivatives in hospitalized adults.

BACKGROUND: A history (or lack thereof) of penicillin allergy is known to be unreliable in predicting reactions on subsequent administration of the drug. This study tests the usefulness of four penicillin allergen skin tests in the prediction of IgE-mediated reactions subsequent to administration of penicillin. METHODS: Eight centers cooperated in the National Institute of Allergy and Infectious Diseases trial of the predictive value of skin testing with major and minor penicillin derivatives. Hospitalized adults were tested with a major determinant (octa-benzylpenicilloyl-ocytalysine) and a minor determinant mixture and its components (potassium benzylpenicillin, benzylpenicilloate, and benzylpenicilloyl-N-propylamine). Patients then received a therapeutic course of penicillin and were observed, for 48 hours, for adverse reactions compatible with an IgE-mediated immediate or accelerated allergy. RESULTS: Among 726 history-positive patients, 566 with negative skin tests received penicillin and only seven (1.2%) had possibly IgE-mediated reactions. Among 600 history-negative patients, 568 with negative skin tests received penicillin and none had a reaction. Only nine of the 167 positive skin test reactors received a penicillin agent and then usually by cautious incremental dosing. Two (22%) of these nine patients had reactions compatible with IgE-mediated immediate or accelerated penicillin allergy; both were positive to the two determinants. CONCLUSIONS: These data corroborate previous data about the negative predictive value of negative skin tests to these materials. The reaction rate in skin test-positive patients was significantly higher than in those with negative skin tests, demonstrating the positive predictive value of positive tests to both major and minor determinants. The number of patients positive only to the major determinant or only to the minor determinant mix was too small to draw conclusions about the positive predictive value of either reagent alone.

Adult↗

Adult onset neurological disorders. Predictive genetic testing.

BACKGROUND: With the rapid advances in gene discovery and genetic diagnosis, increasing numbers of hereditary adult onset neurological disorders can be diagnosed prior to the onset of symptoms. Such testing is called predictive or presymptomatic testing. OBJECTIVE: To present current practice for predictive testing for adult onset neurological disorders and the rationale behind it. DISCUSSION: Predictive testing should be undertaken in the setting of a formal counselling process both before and after results are given. Counselling incorporates genetic information and social and legal repercussions of taking a predictive genetic test. For predictive genetic testing to be possible, the causative mutation in the family must be known. The majority of those at risk of adult onset incurable neurodegenerative disorders choose not to have predictive testing.

Adult↗

"Genetic exceptionalism" in medicine: clarifying the differences between genetic and nongenetic tests.

Predictive genetic tests are now available for assessing susceptibility to a variety of conditions, including breast and colon cancer, hemochromatosis, and Alzheimer and Huntington disease. Much controversy surrounds the application of these tests, stemming from their similarities to and differences from other tests commonly used in asymptomatic persons. Some have argued that genetic tests are unique and therefore justify special consideration with regard to informed consent and privacy. This paper examines the arguments for such "genetic exceptionalism" and concludes that no clear, significant distinctions between genetic and nongenetic tests justify a different approach to testing by clinicians. Nevertheless, with many genetic tests, the results may cause stigmatization, family discord, and psychological distress. Regardless of whether a test is genetic, when this combination of characteristics is present and when health care providers are not specifically trained to interpret results, testing should be performed with particular caution and the highest standards of informed consent and privacy protection should be applied.

Ethics, Medical↗

Predictability of conventional tests for the assessment of bladder outlet obstruction in benign prostatic hyperplasia.

BACKGROUND: The degree of bladder outlet obstruction (BOO) in benign prostatic hyperplasia (BPH) is most accurately quantified by pressure flow studies (PFS), although these studies are more invasive and complicated than conventional tests. We examined how precisely conventional tests predicted the PFS-assessed degree of BOO. METHODS: The study population consisted of 232 BPH patients who had undergone routine conventional tests and PFS. Correlation of the conventional test results with the degree of BOO assessed by PFS was examined by Spearman's correlation coefficients. Regression and subgroup analyses were performed to predict the degree of BOO using the conventional test results as the explanatory variables. RESULTS: The degree of BOO correlated with prostate volume, the degree of endoscopic obstruction, and to a lesser extent, with the maximum flow rate (Qmax) and age. The predictability of conventional tests alone, or in combination, for BOO, was approximately 60% to 70%, which is not acceptable for investigational use. However, almost all patients with a prostate volume larger than 30 mL, or with severe obstruction on urethroscopic findings, had an obstructed bladder outlet. CONCLUSION: PFS is mandatory when the precise evaluation of the degree of BOO is required, and patients are highly likely to have an outlet obstruction when they have a prostate larger than 30 mL, or severely obstructed posterior urethra on endoscopy.

Aged↗

Predictive genetic test decisions for Huntington's disease: context, appraisal and new moral imperatives.

Predictive testing is one of the new genetic technologies which, in conjunction with developing fields such as pharmacogenomics, promises many benefits for preventive and population health. Understanding how individuals appraise and make genetic test decisions is increasingly relevant as the technology expands. "Lay" understandings of genetic risk and test decision-making, located within holistic life frameworks including family or kin relationships, may vary considerably from clinical representations of these phenomena. The predictive test for Huntington's disease (HD), whilst specific to a single-gene, serious, mature-onset but currently untreatable disorder, is regarded as a model in this context. This paper reports upon a qualitative Australian study which investigated predictive test decision-making by individuals at risk for HD, the contexts of their decisions and the appraisals which underpinned them. In-depth interviews were conducted in Australia with 16 individuals at 50% risk for HD, with variation across testing decisions, gender, age and selected characteristics. Findings suggested predictive testing was regarded as a significant life decision with important implications for self and others, while the right "not to know" genetic status was staunchly and unanimously defended. Multiple contexts of reference were identified within which test decisions were located, including intra- and inter-personal frameworks, family history and experience of HD, and temporality. Participants used two main criteria in appraising test options: perceived value of, or need for the test information, for self and/or significant others, and degree to which such information could be tolerated and managed, short and long-term, by self and/or others. Selected moral and ethical considerations involved in decision-making are examined, as well as the clinical and socio-political contexts in which predictive testing is located. The paper argues that psychosocial vulnerabilities generated by the availability of testing technologies and exacerbated by policy imperatives towards individual responsibility and self-governance should be addressed at broader societal levels.

Adult↗

Expanded experience with an intradermal skin test to predict for the presence or absence of carboplatin hypersensitivity.

PURPOSE: Carboplatin-associated hypersensitivity is increasingly recognized as a potentially serious toxicity when this agent is administered for more than six total cycles. PATIENTS AND METHODS: Our group has used a predictive skin test in women with gynecologic cancers who have previously received more than six cumulative cycles of platinum-based chemotherapy. Thirty minutes before all subsequent carboplatin courses, a 0.02-mL aliquot from the solution prepared for treatment is injected intradermally. A positive test is considered to be a > or = 5-mm wheal, with a surrounding flare. RESULTS: From October 1998 through March 2003, 126 patients received a total of 717 carboplatin skin tests (median per patient, four tests; range, one to 54 tests). Of the 668 negative tests (93% of the total performed), 10 were associated with evidence of carboplatin hypersensitivity (1.5% false-negative rate; 95% CI, 0.6% to 2.4%), none of which were severe (eg, dyspnea, hypotension, cardiac/respiratory compromise). Of the 41 positive tests, the decision was made to not deliver the drug to 32 patients, although seven women ultimately underwent a future attempt at re-treatment with a platinum agent using a desensitization program. In seven episodes where patients received the carboplatin despite the finding of a positive test, six were associated with the development of symptoms of anaphylaxis (none severe). CONCLUSION: A negative carboplatin skin test seems to predict with reasonable reliability for the absence of a severe hypersensitivity reaction with the subsequent drug infusion. The implications of a positive test remain less certain, but limited experience with continued treatment suggests this approach must be undertaken with considerable caution.

Adult↗

Fetal acoustic stimulation testing. III. Predictive value of a reactive test.

The nonstress test (NST) is a helpful adjunct to the management of high-risk pregnancies. However, fetal sleep states may lead to falsely nonreactive tests. We assessed the usefulness of transabdominal acoustic stimulation of the fetus and demonstrated an approximately 50% reduction in the number of nonreactive tests and a shorter testing time. No change in the predictive reliability of a reactive test was observed. With regard to the intrapartum and neonatal outcome in women delivering within seven days of a reactive test, no difference between the incidence of meconium-stained amniotic fluid, depressed one- or five-minute Apgar scores or operative intervention for fetal distress could be identified. A reactive test evoked by acoustic stimulation is as reliable as the NST. It offers the additional benefits of reduced testing time and a lower incidence of nonreactive tests.

Acoustic Stimulation↗