Consulting the source code: prospects for gene-based medical diagnostics

Identical but not the same: the value of discordant monozygotic twins in genetic research

Monozygotic (MZ) twins show remarkable resemblance in many aspects of behavior, health, and disease. Until recently, MZ twins were usually called "genetically identical"; however, evidence for genetic and epigenetic differences within rare MZ twin pairs has accumulated. Here, we summarize the literature on MZ twins discordant for Mendelian inherited disorders and chromosomal abnormalities. A systematic literature search for English articles on discordant MZ twin pairs was performed in Web of Science and PubMed. A total number of 2,016 publications were retrieved and reviewed and 439 reports were retained. Discordant MZ twin pairs are informative in respect to variability of phenotypic expression, pathogenetic mechanisms, epigenetics, and post-zygotic mutagenesis and may serve as a model for research on genetic defects. The analysis of single discordant MZ twin pairs may represent an elegant approach to identify genes in inherited disorders.

Texas physicians' perceptions of genomic medicine as an innovation

Primary care providers (PCPs) are believed to be the professionals who, in the near future, will be responsible for incorporating genomic medicine (GM) into primary care. Given the dearth of empirical data describing PCPs' beliefs about GM and the relationship between beliefs and the incorporation of GM into practice, this study assessed whether (and to what extent) PCPs' perceptions of GM as an innovation influence their likelihood of adopting this innovation into primary care. The study utilized diffusion of innovations theory as a framework. A state-wide representative sample of PCPs practicing in Texas responded to a mailed survey. The survey measured PCPs' perceptions of five characteristics of GM as an innovation. Findings suggest that among the five characteristics examined GM's relative advantage, compatibility with current practice, its complexity, and observability were the strongest predictors of likelihood to adopt GM tasks into primary care practice.

Collaborative strategies for unraveling the complexity of birth defects

This article summarizes a presentation by one of the authors (CAH) to the Fifth Annual Meeting of the Diabetes in Pregnancy Study Group of North America. Dr Hobbs, MD, PhD, the Director of the Arkansas Center for Birth Defects Research and Prevention, presented an overview of the collaborative strategies developed for investigating the etiology of birth defects. A multidisciplinary group of scientists and clinicians explores current hypotheses in diabetic embryopathy, drawing upon expertise in experimental biology, genetic epidemiology, genomics, metabolomics and translational research. The prevalence rate of birth defects among infants of diabetic mothers is as high as 11%, despite the knowledge that maternal metabolic control is strongly correlated with the risk of malformations. Specifically, caudal dysgenesis, renal anomalies, heart and neural tube defects and situs abnormalities occur more often among infants of diabetic women than non-diabetic women. Researchers are also working to discover the underlying mechanisms that make some women with diabetes more susceptible than others to having infants with birth defects.

Familial Frontotemporal Dementia: From Gene Discovery to Clinical Molecular Diagnostics

Genetic testing is important for diagnosis and prediction of many diseases. The development of a clinical genetic test can be rapid for common disorders, but for rare genetic disorders this process can take years, if it occurs at all. We review the path from gene discovery to development of a clinical genetic test, using frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17) as an example of a complex, rare genetic condition. An Institutional Review Board-approved multidisciplinary research program was developed to identify patients with familial frontotemporal dementia. Genetic counseling is provided and DNA obtained to identify mutations associated with FTDP-17. In some cases it may be appropriate for individuals to be given the opportunity to learn information from the research study to prevent unnecessary diagnostic studies or the utilization of inappropriate therapies, and to make predictive testing possible. Mutations identified in a research laboratory must be confirmed in a clinical laboratory to be used clinically. To facilitate the development of clinical genetic testing for a rare disorder, it is useful for a research laboratory to partner with a clinical laboratory. Most clinical molecular assays are developed in research laboratories and must be properly validated. We conclude that the transition of genetic testing for rare diseases from the research laboratory to the clinical laboratory requires a validation process that maintains the quality-control elements necessary for genetic testing but is flexible enough to permit testing to be developed for the benefit of patients and families.

Prenatal diagnosis: molecular genetics and cytogenetics

The technologies developed for the Human Genome Project, the recent surge of available DNA sequences resulting from it and the increasing pace of gene discoveries and characterization have all contributed to new technical platforms that have enhanced the spectrum of disorders that can be diagnosed prenatally. The importance of determining the disease-causing mutation or the informativeness of linked genetic markers before embarking upon a DNA-based prenatal diagnosis is, however, still emphasized. Different fluorescence in situ hybridization (FISH) technologies provide increased resolution for the elucidation of structural chromosome abnormalities that cannot be resolved by more conventional cytogenetic analyses, including microdeletion syndromes, cryptic or subtle duplications and translocations, complex rearrangements involving many chromosomes, and marker chromosomes. Interphase FISH and the quantitative fluorescence polymerase chain reaction are efficient tools for the rapid prenatal diagnosis of selected aneuploidies, the latter being considered to be most cost-effective if analyses are performed on a large scale. There is some debate surrounding whether this approach should be employed as an adjunct to karyotyping or whether it should be used as a stand-alone test in selected groups of women.