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Presymptomatic testing for genetic diseases of later life. Pharmacoepidemiological considerations.

As the Human Genome Project gathers speed, new disease genes are rapidly being found. Important as these discoveries are, they are only the beginning of the process of characterising, diagnosing and treating genetic diseases. We now have the potential to predict the onset of many disorders before the appearance of clinical symptoms, even though treatment is not always available. In this review we have used a number of examples to illustrate various aspects of the presymptomatic diagnosis of genetic disease and, where possible, late-onset disorders have been chosen as examples. When treatment is available, the diagnosis of a disease before appearance of symptoms can greatly improve the prognosis. When treatment is not available, reasons to undergo presymptomatic testing may not be so obvious. However, appropriate lifestyle changes or medical surveillance can sometimes delay onset or decrease severity of a disorder. Even if no treatment is available, genetic testing and counselling for the patient and family members can provide useful information for future planning.

Aged↗

Detection of heterozygous C8 beta deficiency by PCR in a healthy Italian population.

In Italy a rather high number of homozygotes with late complement component defects has been found among patients with meningococcal disease. It seems that clinical manifestations of meningococcal disease are less severe in patients with complement deficiency than in normal individuals. This situation could even be more evident in the heterozygous carriers for whom a selective advantage is discussed. In this study we have screened a cohort of 527 Italian blood donors from western Sicily for the presence of C8B mutated allele. Heterozygotes for C8 beta deficiency were identified using a specific PCR assay to detect a C-->T transition in exon 9 of the C8B gene. This mutation represents the most frequent genetic mechanism for C8 beta deficiency in Caucasians. A rapid PCR screening test was performed on DNA extracted from pooled blood samples of up to 8 individuals. A single male individual with heterozygous C8 beta deficiency was detected. In the family studies it was shown that his two brothers and the mother were heterozygous carriers too. Functional activity of the classical and alternative complement pathways were normal. No neisserial infections or inflammatory diseases were found in the family history. It was shown that the allele-specific PCR is a sensitive and rapid method to examine large numbers of DNA samples. It permitted to assess the real prevalence of the C8B mutated null allele in the general population free of ascertainment bias.

Alleles↗

A quick and simple method for detecting subjects with abnormal genetic background in case-control samples.

It is important that case-control samples be drawn from a genetically homogeneous population in order to avoid artefactual false positive results and to enhance power to detect disease mutations and markers in linkage disequilibrium with them. Tests which simply compare overall marker allele frequencies between cases and controls will fail to identify a relatively small number of subjects drawn from a different genetic background who could usefully be discarded from the sample. Such subjects can be identified using multilocus tests, but previously described tests have been unnecessarily complex and cumbersome for this simple application. We describe a straightforward test, implemented in the CHECKHET program, which uses a measure of genetic difference and permutation procedures to rapidly identify such subjects using genotypes from multiple unlinked markers. It seems to perform reasonably well on simulated data, and with real data appears to identify two abnormal subjects within a case-control sample. We recommend that such tests be routinely applied to case-control samples once sufficient numbers of markers have been genotyped within them.

Case-Control Studies↗

Pilot studies for proficiency testing using fluorescence in situ hybridization with chromosome-specific DNA probes: a College of American Pathologists/American College of Medical Genetics Program.

Fluorescence in situ hybridization using chromosome-specific DNA probes is rapidly becoming part of clinical laboratory practice for certain congenital and neoplastic disorders. Current legislation requires proficiency testing for clinical laboratory studies. To evaluate the efficacy of fluorescence in situ hybridization proficiency testing, we invited 19 representative institutions to participate in three pilot studies. One study used probes for the X and Y chromosomes to evaluate metaphase spreads and interphase nuclei. Another study used probes for bcr and abl to detect bcr/abl fusion in interphase nuclei in chronic myelogenous leukemia. The third study used a D22S75 probe to detect microdeletions in metaphase spreads from a patient with velocardiofacial syndrome. The results of these studies demonstrate that proficiency testing with fluorescence in situ hybridization is attainable using either metaphase or interphase preparations, and that either microscope slides or fixed cell pellets are suitable.

Chromosome Mapping↗

Practical aspects of mutagenicity testing strategy: an industrial perspective.

Genetic toxicology studies play a central role in the development and marketing of new chemicals for pharmaceutical, agricultural, industrial, and consumer use. During the discovery phase of product development, rapid screening tests that require minimal amounts of test materials are used to assist in the design and prioritization of new molecules. At this stage, a modified Salmonella reverse mutation assay and an in vitro micronucleus test with mammalian cell culture are frequently used for screening. Regulatory genetic toxicology studies are conducted with a short list of compounds using protocols that conform to various international guidelines. A set of four assays usually constitutes the minimum test battery that satisfies global requirements. This set includes a bacterial reverse mutation assay, an in vitro cytogenetic test with mammalian cell culture, an in vitro gene mutation assay in mammalian cell cultures, and an in vivo rodent bone marrow micronucleus test. Supplementary studies are conducted in certain instances either as a follow-up to the findings from this initial testing battery and/or to satisfy a regulatory requirement. Currently available genetic toxicology assays have helped the scientific and industrial community over the past several decades in evaluating the mutagenic potential of chemical agents. The emerging field of toxicogenomics has the potential to redefine our ability to study the response of cells to genetic damage and hence our ability to study threshold phenomenon.

Guidelines as Topic↗

Phenotypic and genetic differentiation between native and introduced plant populations.

Plant invasions often involve rapid evolutionary change. Founder effects, hybridization, and adaptation to novel environments cause genetic differentiation between native and introduced populations and may contribute to the success of invaders. An influential idea in this context has been the Evolution of Increased Competitive Ability (EICA) hypothesis. It proposes that after enemy release plants rapidly evolve to be less defended but more competitive, thereby increasing plant vigour in introduced populations. To detect evolutionary change in invaders, comparative studies of native versus introduced populations are needed. Here, we review the current empirical evidence from: (1) comparisons of phenotypic variation in natural populations; (2) comparisons of molecular variation with neutral genetic markers; (3) comparisons of quantitative genetic variation in a common environment; and (4) comparisons of phenotypic plasticity across different environments. Field data suggest that increased vigour and reduced herbivory are common in introduced plant populations. In molecular studies, the genetic diversity of introduced populations was not consistently different from that of native populations. Multiple introductions of invasive plants appear to be the rule rather than the exception. In tests of the EICA hypothesis in a common environment, several found increased growth or decreased resistance in introduced populations. However, few provided a full test of the EICA hypothesis by addressing growth and defence in the same species. Overall, there is reasonable empirical evidence to suggest that genetic differentiation through rapid evolutionary change is important in plant invasions. We discuss conceptual and methodological issues associated with cross-continental comparisons and make recommendations for future research. When testing for EICA, greater emphasis should be put on competitive ability and plant tolerance. Moreover, it is important to address evolutionary change in characteristics other than defence and growth that could play a role in plant invasions.

Adaptation, Physiological↗

In utero delivery of adeno-associated viral vectors: intraperitoneal gene transfer produces long-term expression.

Recombinant adeno-associated viruses (rAAV) are promising gene transfer vectors that produce long-term expression without toxicity. To investigate future approaches for in utero gene delivery, the efficacy and safety of prenatal administration of rAAV were determined. Using luciferase as a reporter, expression was assessed by whole-body imaging and by analysis of luciferase activity in tissue extracts, at the time of birth and monthly thereafter. Transgene expression was detected in all injected animals. Highest levels of luciferase activity were detected at birth in the peritoneum and liver, while the heart, brain, and lung demonstrated low-level expression. In vivo luciferase imaging revealed persistent peritoneal expression for 18 months after in utero injection and provided a sensitive whole-body assay, useful in identifying tissues for subsequent analyses. There was no detectable hepatocellular injury. Antibodies that reacted with either luciferase or rAAV were not found. AAV sequences were not detected in germ-line tissues of injected animals or in tissues of their progeny. In utero AAV-mediated gene transfer in this animal model demonstrates that novel therapeutic vectors and strategies can be rapidly tested in vivo and that rAAV may be developed to ameliorate genetic diseases with perinatal morbidity and mortality.

Animals↗

[Diagnosis of transmissible spongiform encephalopathies in Spain. Population perspective].

OBJECTIVES: To describe specific aspects of the diagnostic process of transmissible spongiform encephalopathies in Spain and to evaluate the 14-3-3 protein test in cerebrospinal fluid. METHODS: The annual pattern of diagnostic certainty as well as those of demand and results of biochemical and genetic studies were studied using two sets of patients, those diagnosed for the 1993-1998 period, notified to a National Creutzfeldt-Jakob Disease Register (NCDJR), and those referred to the Tissue Bank for Neurological Research Laboratory (TBNRL). The 14-3-3 protein test was validated taking as a reference two clinical populations. RESULTS: Two-hundred and four Creutzfeldt-Jakob disease cases were registered at the NCDJR: 39 out of them and 28 other patients had been studied at the TBNRL. The proportion of definite Creutzfeldt-Jakob Disease cases decreased since 1996. Among those registered in 1997-1998, 35.5%, 36% and 20% had undergone 14-3-3 protein in LCR, histopathologic and genetic studies. The 14-3-3 test grave, for definite, sporadic Creutzfeldt-Jakob disease as compared for patients with other dementing disorders, the following data: 12/13 sensitivity; 33/35 specificity; and 12/14 and 33/34 predictive values of positive and negative test. Two familial cases were diagnosed by identification of mutations in the TBNRL. CONCLUSIONS: The results suggest that: a) the diagnostic certainty of Creutzfeldt-Jakob disease in Spain decreased due to a drop in autopsy rates; b) the 14-3-3 cerebrospinal fluid test has a high diagnostic value, and its use diffused rapid but incompletely; c) genetic studies are useful in some cases, and d) Creutzfeldt-Jakob disease undereporting may be considerable. Creutzfeldt-Jakob disease diagnosis and surveillance, are closely related and being consolidated in Spain.

Creutzfeldt-Jakob Syndrome↗

Micronuclei in circulating erythrocytes: a rapid screen for chromosomal damage during routine toxicity testing in mice.

Micronuclei in circulating erythrocytes provide a convenient measure of genetic damage resulting from chromosomal breakage or anaphase lag in bone marrow erythroblasts. The assay is easily integrated with acute, subchronic, or chronic toxicity tests. Scoring micronucleated erythrocytes in blood rather than bone marrow permits repeated sampling, simplifies sample preparation, and provides a more favorable cell population for scoring. Micronucleated erythrocytes accumulate during repeated exposures to clastogens and reach a maximum steady-state frequency after about five weeks of continuous treatment. Measurement of micronuclei in peripheral blood is therefore ideally suited for inclusion with routine subchronic toxicity tests. The same smear made for differential white blood cell counts at or near the end of the study can be scored for micronucleated erythrocytes, minimizing the effort required for this additional information and also permitting retrospective evaluation of completed studies.

Animals↗

Psychosocial aspects of risk communication and mutation testing in familial breast-ovarian cancer.

PURPOSE OF REVIEW: As cancer genetics services develop, psychosocial research evaluating risk communication and mutation testing for familial breast-ovarian cancer has expanded rapidly. It is timely to review findings in key areas. These will inform risk counselling practice and help prepare women making risk management decisions. RECENT FINDINGS: The psychological effect of risk communication and genetic counselling has been elucidated and women's risk perceptions explored. Knowledge of optimal risk communication strategies is lacking, but recent research shows both consistency in information giving and deficiencies in specific communication skills; the need for personally tailored risk information, which addresses counsellees' concerns, is highlighted. Outcome assessments of risk communication, such as risk perception and psychological distress, are useful but insufficient to evaluate the complex communication process, and decision making in this context is underresearched. Subsequent diffusion of risk information and interfamily communication pose difficulties for high-risk individuals. The short-term psychological consequences of predictive mutation testing are an important focus of research and are largely reassuring, but long-term outcomes are sparse. SUMMARY: Our understanding of the psychological benefits and limitations of risk counselling and mutation testing can now inform clinical practice, but insufficient knowledge exists of long-term outcomes. Most women are unlikely to be distressed following risk communication, but some may need psychosocial support in the short term following predictive testing for BRCA1/2. Different approaches to risk communication need to be developed and evaluated in parallel with communications skills training to ensure an adequate focus on the women's agenda.

Breast Neoplasms↗

The rapid analysis of dystrophin gene deletions shows variable electrophoretic mobility.

The introduction of PCR technology to the molecular diagnosis of genetic diseases has increased the speed and range of DNA tests available. Previous analyses of dystrophin gene mutations were time consuming, taking weeks to complete, and used radioisotopic methods. Further developments in DNA amplification and post-amplification techniques have made conventional tube PCR redundant. The rapid methodologies described enable the efficient screening of large populations for genetic disorders, although precautions must be taken when analysing the PCR products.

Cross-Linking Reagents↗

A biosensor for environmental genotoxin screening based on an SOS lux assay in recombinant Escherichia coli cells.

A genetically controlled luminescent bacterial reporter assay, the SOS lux test, was developed for rapid detection of environmental genotoxins. The bioassay is based on the recombinant plasmid pPLS-1, which was constructed as a derivative of pBR322, carrying the promoterless luxCDABFE genes of Photobacterium leiognathi downstream of a truncated cda gene from ColD with a strong SOS promoter. E. coli recA+ strains containing this construction are inducible to high levels of light production in the presence of substances or agents that cause damage to the DNA of the cells. The light signal, reflecting the SOS-inducing potency, is recorded from the growing culture within 1 s, and the test results are available within 1 to 2 h. Induction of bioluminescence was demonstrated by treatment of E. coli C600(pPLS-1) with 6 genotoxic chemicals (mitomycin C, N-methyl-N'-nitro-N-nitrosoguanidine, nalidixic acid, dimethylsulfate, hydrogen peroxide, and formaldehyde) and with UV and gamma radiation. A clear dose-response relationship was established for all eight genotoxins. The sensitivity of the SOS lux test is similar to that of other bioassays for genotoxicity or mutagenicity, such as the SOS chromotest, umu test, and Ames mutatest. These results indicate that the SOS lux test is potentially useful for the in situ and continuous detection of genotoxins.

Base Sequence↗

Issues in the genetic assessment of predispositions for familial breast and ovarian cancer.

A rapid development in technology has enabled predictive testing for cancer suceptibility genes, such as BRCA1 and BRCA2. Already biotechnology companies and a number of university-based researchers are establishing service laboratories for the analysis of cancer predispositions. It is critical that high standards be established and maintained when conducting DNA testing, which should be performed in a research setting with proper Institutional Review Board approval. A cancer risk assessment programme should include the involvement of various experts in genetics, oncology, psychiatry and counselling. The legal, ethical and social issues involved in screening and testing for cancer predisposition genes are complex. Genetic counselling of subjects undergoing testing is needed to inform them of the potential risks as well as the potential benefits associated with presymptomatic testing.

Breast Neoplasms↗

Genetic mechanisms and mental retardation.

The past five years have witnessed rapid and apparently relentless progress in the delineation of the genetic basis of disorders associated with mental retardation. Each gene discovery has a new story to tell but inevitably generates further questions. For the clinical geneticist and, perhaps more importantly, for patients and their families, many of these recent discoveries have yielded information which has immediate implications for diagnostic testing, family and population screening and prenatal testing. Many of the ethical issues consequent upon the rapid progress are only now being addressed. This article highlights a number of disorders whose molecular genetic basis has recently been further characterised. Brain development and maintenance of neurological networks provide the unifying theme; the genetic defects are disparate and each of their mechanisms appears to be novel.

Chromosome Deletion↗

Procreative beneficence: why we should select the best children.

Eugenic selection of embryos is now possible by employing in vitro fertilization (IVF) and preimplantation genetic diagnosis (PGD). While PGD is currently being employed for the purposes of detecting chromosomal abnormalities or inherited genetic abnormalities, it could in principle be used to test any genetic trait such as hair colour or eye colour. Genetic research is rapidly progressing into the genetic basis of complex traits like intelligence and a gene has been identified for criminal behaviour in one family. Once the decision to have IVF is made, PGD has few 'costs' to couples, and people would be more inclined to use it to select less serious medical traits, such as a lower risk of developing Alzheimer Disease, or even for non-medical traits. PGD has already been used to select embryos of a desired gender in the absence of any history of sex-linked genetic disease. I will argue that: (1) some non-disease genes affect the likelihood of us leading the best life; (2) we have a reason to use information which is available about such genes in our reproductive decision-making; (3) couples should select embryos or fetuses which are most likely to have the best life, based on available genetic information, including information about non-disease genes. I will also argue that we should allow selection for non-disease genes even if this maintains or increases social inequality. I will focus on genes for intelligence and sex selection. I will defend a principle which I call Procreative Beneficence: couples (or single reproducers) should select the child, of the possible children they could have, who is expected to have the best life, or at least as good a life as the others, based on the relevant, available information.

Beneficence↗

Genetic toxicology of acrylic acid.

Acrylic acid was tested for gene mutations in the in vitro CHO/HGPRT assay, for chromosome aberrations in CHO cells in culture, and for potential to induce unscheduled DNA synthesis in rat hepatocytes in culture. In vivo assays performed included the Drosophila sex-linked recessive lethal assay by both the feeding and injection routes, the in vivo cytogenetic assay in rat bone marrow cells after both a 1-day and 5-day oral dosing regimen, and a dominant lethal assay in mice by both an acute and 5-day dosing regimen. All results were negative (non-mutagenic) except for the in vitro chromosome aberration assay. This latter result is consistent with the previously reported possible clastogenic activity suggested by the results of the mouse lymphoma L5178Y TK locus assay in which a predominance of small-colony mutants was observed (Moore et al., Environmental and Molecular Mutagenesis 1988, 11, 49-63). The rapid clearance of acrylic acid in animals and the weight of evidence of genetic toxicity testing, including negative in vivo data in both somatic and germ cells, indicate a lack of genetic toxicity of acrylic acid in vivo.

Acrylates↗

Pharmacogenetics and cardiovascular disease: impact on drug response and applications to disease management.

The genetic polymorphisms that may affect individual responses to cardiovascular agents are reviewed, and the application of pharmacogenetics to cardiovascular disease management is discussed. Pharmacogenetics is the search for genetic polymorphisms that affect responses to drug therapy. Investigators have found many associations between genetic polymorphisms and responses to cardiovascular drugs. Some of these relationships have been demonstrated in large patient populations, such as patients with ischemic heart disease receiving statins. Study data consistently show a greater response to statins in ischemic heart disease patients with genotypes associated with worse prognoses. Studies of other polymorphisms, such as those in the genes encoding anglotensin-converting enzyme and beta 1-adrenergic receptors, have less consistently found relationships between these variations and cardiovascular drug responses. For gene-drug response associations for which the data are inconsistent, the interaction of multiple polymorphisms in multiple genes coding for proteins affected by drug therapy or influencing drug metabolism may prove to have a greater influence on drug responses than any one polymorphism. Once the polymorphisms that best determine the response to a particular drug are known and tests to rapidly identify these variations are available, individual patients may be screened for genetic polymorphisms before drug therapy is begun and the information used to choose agents with the greatest potential for efficacy and least potential for toxicity. Pharmacogenetics has many possible applications in the drug therapy of cardiovascular diseases. Much more must be learned, however, before pharmacogenetic factors can be routinely incorporated into therapeutic decisions.

Cardiovascular Agents↗

Ultra-rapid DNA analysis using HyBeacon probes and direct PCR amplification from saliva.

We describe a novel probe technology, termed HyBeacons, which provides a new homogeneous method for fluorescence-based sequence detection and allele discrimination. Employing a single nucleotide polymorphism located in the N-acetyltransferase 2 gene as a model system, we demonstrate the utility of HyBeacon probes for rapid and reliable sequence analysis. We also demonstrate that homozygous and heterozygous samples may be accurately identified using a single HyBeacon oligonucleotide. Polymorphic DNA sequences were detected and differentiated by real-time PCR and melt peak methodologies, without performing extraction of genomic DNA prior to target amplification. Employing a combination of homogeneous HyBeacon analysis, the rapid thermal cycling conditions of the LightCycler and direct amplification from saliva, allowed samples to be genotyped within 30 min. Such rapid non-invasive diagnostic technologies may permit 'point-of-care' genetic testing to be performed in hospitals and doctor's surgeries.

Arylamine N-Acetyltransferase↗