Molecular mechanisms in neurologic disorders

Epigenetic transgenerational toxicology and germ cell disease

The ability of an environmental exposure (i.e. endocrine disruptor) during sex determination to reprogramme the male germline and promote an epigenetic transgenerational disease phenotype suggests that environmental factors and compounds may permanently alter the germline epigenome. This epigenetic transgenerational phenomenon will be discussed with respect to adult-onset germline disease (e.g. testicular cancer). A thorough literature review is not provided, rather a perspective is provided on how this epigenetic transgenerational toxicology should be considered in germ cell disease and testicular cancer.

Down syndrome with an unusual etiology: case report and review

PURPOSE

To present the genetic etiology of an unusual case of Down syndrome, arising from translocation of chromosome 21 to chromosome 9; to discuss advanced genetic diagnostic techniques, focusing on how pinpointing a specific genetic mistake can influence treatment and outcome; and to review the role of the nurse practitioner (NP) in caring for families of children with Down syndrome.

DATA SOURCES

Case report, literature review, and advanced genetic techniques.

CONCLUSIONS

NPs often answer patient questions regarding genetic abnormalities and risk factors for transmission of genetic errors to offspring. Advanced genetic analysis allows for the diagnosis of unusual causes of common genetic disorders. The ability to identify a specific genetic mistake and to predict the scope of its effect on an individual offers health care providers the opportunity to develop a case-by-case plan of care.

IMPLICATIONS FOR PRACTICE

NPs have a responsibility to be informed about the processes involved in the transmission of genetic errors and about the subtleties of various expressions of a genetic disorder. The availability of new genetic-testing techniques allows NPs to individualize patient care and family teaching.

An Analysis of Microsatellite Loci in Arabidopsis thaliana: Mutational Dynamics and Application

Microsatellite loci are among the most commonly used molecular markers. These loci typically exhibit variation for allele frequency distribution within a species. However, the factors contributing to this variation are not well understood. To expand on the current knowledge of microsatellite evolution, 20 microsatellite loci were examined for 126 accessions of the flowering plant, Arabidopsis thaliana. Substantial variability in mutation pattern among loci was found, most of which cannot be explained by the assumptions of the traditional stepwise mutation model or infinite alleles model. Here it is shown that the degree of locus diversity is strongly correlated with the number of contiguous repeats, more so than with the total number of repeats. These findings support a strong role for repeat disruptions in stabilizing microsatellite loci by reducing the substrate for polymerase slippage and recombination. Results of cluster analyses are also presented, demonstrating the potential of microsatellite loci for resolving relationships among accessions of A. thaliana.

Pharmacology of neural tube defects

The pharmacology of neural tube defects (NTDs) is a complex issue. Several theories regarding the etiology of NTDs emphasize the importance of interactions between genetic, environmental, and biochemical factors at a key point in time. One such factor is chronic drug therapy, a potential consequence of which is the formation of toxic drug metabolites, including free radicals (FRs), which have been implicated in the etiology of NTDs. Under normal physiological conditions, FRs are quickly destroyed by antioxidant defense systems. However, FR-mediated cellular damage can occur if these defense systems fail or are overburdened, such as in patients who are genetically deficient in FR scavenging enzyme activity (FRSEA) or who are receiving chronic drug therapy. Congenital defects, including NTDs, resulting from FR-induced damage have been reported in both experimental animals and humans. For example, the use of antiepileptic drugs (AEDs) during pregnancy that have the propensity to form FRs during their metabolism are associated with an increased risk of the development of congenital malformations, including NTDs. This article reviews the biochemistry of FRs, the factors regulating FR scavenging capacity, and the theories regarding the etiology of NTDs; presents a hypothesis of a unified mechanism for AED-induced NTDs and other congenital defects; and briefly discusses the roles of folate and selenium in the prevention of NTDs.

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.