Insights into the genetic basis of congenital heart disease

Cardiovascular malformations are the most common type of birth defect and result in significant mortality worldwide. The etiology for the majority of these anomalies remains unknown. Advances in the characterization of the molecular pathways critical for normal cardiac development have led to the identification of numerous genes necessary for this complex morphogenetic process. This work has aided the discovery of an increasing number of single genes being implicated as the cause of human cardiovascular malformations. This review summarizes normal cardiac development and outlines the recent discoveries of the genetic causes of congenital heart disease. Received 4 November 2005; received after revision 14 January 2006; accepted 1 February 2006     

The human genome and understanding of common disease: present and future technologies

The study of candidate genes over the past three decades has yielded notable successes in common-disease genetics. During this time, however, interpretation of genetic association studies has been hampered by the use of clinical cohorts of inadequate power and insufficient information on genetic variation in candidate genes. The unavailability of highthroughput and low-cost genotyping technologies has also limited the scope of complex-disease genetic studies. More recently, however, the sequencing and characterization of variation within the human genome has revolutionized genetic studies and enabled full genome-wide scans for genes associated with disease. The identification of disease-associated (causative) genes has illuminated disease mechanisms. The translation of this knowledge into direct clinical benefit in diagnosis, prognosis and therapy for an individual’s disease still remains a challenge. Received 11 September 2006; received after revision 17 December 2006; accepted 18 January 2007     

Genetic susceptibility to hypertensive renal disease

Hypertensive renal disease occurs at increased frequency among the relatives of patients with this disease compared to individuals who lack a family history of disease. This suggests a heritable risk in which genetic variation may play a role. These observations have motivated a search for genetic variation contributing to this risk in both experimental animal models and in human populations. Studies of animal models indicate the capacity of natural genetic variants to contribute to disease risk and have produced a few insights into the disease mechanism. In its current phase, human population genetic studies have sought to associate genetic variation with disease in large populations by testing genotypes at a large number of common genetic variations in the genome, expecting that common genetic variants contributing to renal disease risk will be identified. These genome-wide association studies (GWAS) have been productive and are a clear technical success; they have also identified narrowly defined loci and genes containing variation contributing to disease risk. Further extension and refinement of these GWAS are likely to extend this success. However, it is also clear that few additional variants with substantial effects accounting for the greatest part of heritability will be uncovered by GWAS. This raises an interesting biological question regarding where the remaining unaccounted heritable risk may be located. At present, much consideration is being given to this question and to the challenge of testing hypotheses that lead from the various alternative mechanisms under consideration. One result of the progress of GWAS is likely to be a renewed interest in mechanisms by which related individuals can share and transmit traits independently of Mendelian inheritance. This paper reviews the current progress in this area and considers other mechanisms by which familial aggregation of risk for renal disease may arise.     

The roles of collagen genes in skeletal development and morphogenesis

Molecular genetic analyses of osteochondrodysplasias in mice and humans have recently led to the identification of mutations in genes encoding structural proteins growth factor receptors and sulphate transporters. Further analyses of such inherited disorders, using rapid techniques for gene mapping, positional cloning and mutation detection, will undoubtedly uncover other genes that are important for skeletal development. Together with studies of transgenic mice, in which specific genes that are expressed in the skeleton are mutated, these analyses will provide insight into genes that are essential for skeletal morphogenesis.     

Genome-wide association study to identify SNPs conferring risk of myocardial infarction and their functional analyses

Myocardial infarction might result from the interactions of multiple genetic and environmental factors, none of which can cause disease solely by each of themselves. Although molecular biological studies revealed that a number of proteins are possibly involved in its pathogenesis, little, if any genetic findings have been reported so far. To reveal genetic backgrounds of myocardial infarction, we performed a large-scale, case-control association study using 92,788 gene-based single-nucleotide polymorphism (SNP) markers. We have identified functional SNPs within the lymphotoxin-α gene (LTA) located on chromosome 6p21 that conferred susceptibility to myocardial infarction. Furthermore, we could identify galectin-2 protein as a binding partner of LTA protein. The association study further revealed that a functional SNP in LGALS2 encoding galectin-2, which led to altered secretion of LTA, also indicated a risk of myocardial infarction. A combined strategy of genetic and molecularcellular biological approaches may be useful in clarifying pathogenesis of common diseases.Received 7 March 2005; received after revision 22 April 2005; accepted 25 April 2005     

Recent advances in the genetics of schizophrenia

The genetic etiology of schizophrenia, a common and debilitating psychiatric disorder, is supported by a wealth of data. Review of the current findings suggests that considerable progress has been made in recent years, with a number of chromosomal regions consistently implicated by linkage analysis. Three groups have shown linkage to 1q21-22 using similar models, with HLOD scores of 6.5, 3.2, and 2.4. Other replicated loci include 13q32 that has been implicated by two independent groups with significant HLOD scores (4.42) or NPL values (4.18), and 5p14.1-13.1, 5q21-33, 8p21-22, and 10p11-15, each of which have been reported as suggestive by at least three separate groups. Different studies have also replicated evidence for a modest number of candidate genes that were not ascertained through linkage. Of these, the greatest support exists for the DRD3 (3q13.3), HTR2A (13q14.2), and CHRNA7 (15q13-q14) genes. The refinement of phenotypes, the use of endophenotypes, reduction of heterogeneity, and extensive genetic mapping have all contributed to this progress. The rapid expansion of information from the human genome project will likely further accelerate this progress and assist in the discovery of susceptibility genes for schizophrenia. A greater understanding of disease mechanisms and the application of pharmacogenetics should also lead to improvements in therapeutic interventions. Received 11 May 2001; received after revision: 20 July 2001; accepted 18 September 2001     

Memory

Progress towards amelioration and eventual cure of human cognitive disorders requires understanding the molecular signaling mechanisms that normally govern learning and memory. The fly Drosophila melanogaster has been instrumental in the identification of molecules and signaling pathways essential for learning and memory, because genetic screens have produced mutants in these processes and the system facilitates integrated genetic, molecular, histological and behavioral analyses. We discuss the behavioral paradigms available to assess associative learning and memory in the fly, the contributions learning and memory mutants have made to our understanding of the molecular mechanisms that govern learning and memory, and predictions stemming from the nature of the affected genes. Furthermore, we consider the multiple well-established behavioral assays available and the powerful molecular genetics of the fly with regard to development of models of human cognitive disorders and their pharmacological treatment.     

Human stem cells as a model for cardiac differentiation and disease

Studies on identification, derivation and characterization of human stem cells in the last decade have led to high expectations in the field of regenerative medicine. Although it is clear that for successful stem cell-based therapy several obstacles have to be overcome, other opportunities lay ahead for the use of human stem cells. A more immediate application would be the development of human models for cell-type specific differentiation and disease in vitro. Cardiomyocytes can be generated from stem cells, which have been shown to follow similar molecular events of cardiac development in vivo. Furthermore, several monogenic cardiovascular diseases have been described, for which in vitro models in stem cells could be generated. Here, we will discuss the potential of human embryonic stem cells, cardiac stem cells and the recently described induced pluripotent stem cells as models for cardiac differentiation and disease. Received 07 August 2008; received after revision 26 September 2008; accepted 03 October 2008     

Evolution of bacterial pathogenesis

The evolution of bacteria is associated with continuous generation of novel genetic variants. The major driving forces in this process are point mutations, genetic rearrangements, and horizontal gene transfer. A large number of human and animal bacterial pathogens have evolved the capacity to produce virulence factors that are directly involved in infection and disease. Additionally, many bacteria express resistance traits against antibiotics. Both virulence factors and resistance determinants are subject to intrastrain genetic and phenotypic variation. They are often encoded on unstable DNA regions. Thus, they can be readily transferred to bacteria of the same species or even to non-related prokaryotes. This review article focuses on the main mechanisms of bacterial microevolution responsible for the rapid emergence of variants with novel virulence and resistance properties. In addition, processes of macroevolution are described with special emphasis on gene transfer and fixation of adaptive mutations in the genome of pathogens.     

Bacterial targets and antibiotics: genome-based drug discovery

The requirement for novel classes of antibiotics to combat the emergence of resistant and multi-resistant bacteria has coincided with the completion sequencing of a number of bacterial genomes. The in silico analysis of these genomes coupled with innovative genetic manipulation has already led to the identification of conserved essential (either in vitro or in vivo, depending on the methodology) genes that are potential targets for antibacterial research. New technologies, made possible by access to the genomic sequences, are capable of simultaneously quantifying almost the entire complement of gene products synthesised by bacterial cells. These technologies are opening up the way for the analysis of expression patterns elicited in cells in response to changes in their environment. The integration of these technologies into the drug discovery process is still in its infancy and the potential wealth of information, some of it already available, has yet to be fully realised.     

An eicosanoid-centric view of atherothrombotic risk factors

Cardiovascular disease is the foremost cause of morbidity and mortality in the Western world. Atherosclerosis followed by thrombosis (atherothrombosis) is the pathological process underlying most myocardial, cerebral, and peripheral vascular events. Atherothrombosis is a complex and heterogeneous inflammatory process that involves interactions between many cell types (including vascular smooth muscle cells, endothelial cells, macrophages, and platelets) and processes (including migration, proliferation, and activation). Despite a wealth of knowledge from many recent studies using knockout mouse and human genetic studies (GWAS and candidate approach) identifying genes and proteins directly involved in these processes, traditional cardiovascular risk factors (hyperlipidemia, hypertension, smoking, diabetes mellitus, sex, and age) remain the most useful predictor of disease. Eicosanoids (20 carbon polyunsaturated fatty acid derivatives of arachidonic acid and other essential fatty acids) are emerging as important regulators of cardiovascular disease processes. Drugs indirectly modulating these signals, including COX-1/COX-2 inhibitors, have proven to play major roles in the atherothrombotic process. However, the complexity of their roles and regulation by opposing eicosanoid signaling, have contributed to the lack of therapies directed at the eicosanoid receptors themselves. This is likely to change, as our understanding of the structure, signaling, and function of the eicosanoid receptors improves. Indeed, a major advance is emerging from the characterization of dysfunctional naturally occurring mutations of the eicosanoid receptors. In light of the proven and continuing importance of risk factors, we have elected to focus on the relationship between eicosanoids and cardiovascular risk factors.     

Production of pharmaceutical proteins in milk

There is every reason to expect that it will be possible within the next few years to begin to use farm animals to produce large quantities of some of the human proteins that are needed for the treatment of disease. Revolutionary new opportunities for the production of novel proteins in milk have been created by the development of methods for gene transfer. Exploitation of these opportunities depends upon selection and cloning of milk protein genes and identification of the sequences that govern tissue specific hormonally induced expression in the mammary gland. Studies with three genes, ovine beta-lactoglobulin, rat beta-casein and whey acidic protein of rat and mouse, suggest that they may all meet this requirement. Fragments of the ovine beta-lactoglobulin, murine whey acidic protein and rabbit beta-casein genes have directed production of novel proteins in the milk of transgenic mice, sheep, rabbits and pigs. The proteins were biologically active and usually co-migrated with authentic proteins. In early experiments, protein concentration was low, but our recent observations suggest that fusion genes containing genomic clones direct production of concentrations of protein that are suitable for commercial exploitation. In the longer term, two approaches may offer the potential of more reliable expression. Control elements capable of directing expression that is independent of site of insertion of the gene, but dependent on the number of copies of the gene, have been identified for a small number of genes. The availability of such elements for the milk protein genes would increase the reliability of gene expression considerably. Alternatively, targeted mutation of genes may allow the insertion of coding sequences within an existing gene so avoiding position effects.     

Genetics and molecular pathogenesis of mitochondrial respiratory chain diseases

Dysfunction of the mitochondrial respiratory chain has been recognised as a cause of human disease for over 30 years. Advances in the past 10 years have led to a better understanding of the genetics and molecular pathogenesis of many of these disorders. Over 100 primary defects in mitochondrial DNA (mtDNA) are now implicated in the pathogenesis of a group of disorders which are collectively known as the mitochondrial encephalomyopathies, and which most frequently involve skeletal muscle and/or the central nervous system. Although impaired oxidative phosphorylation is likely to be the final common pathway leading to the cellular dysfunction associated with such mtDNA mutations, the complex relationship between genotype and phenotype remains largely unexplained. Most of the genes which encode the respiratory chain reside in the nucleus, yet only five nuclear genes have been implicated in human respiratory chain diseases. There is evidence that respiratory chain dysfunction is present in common neurological diseases such as Parkinson's disease and Huntington's disease. The precise cause of this respiratory chain dysfunction and its relationship to the disease process are unclear. This review focuses upon respiratory chain disorders associated with primary defects in mtDNA.     

Genetic factors for human obesity

Obesity is a multifactorial and heterogeneous condition that results from alterations of various genes, each having a partial and additive effect. The inheritance pattern of obesity is thus complex, and environmental factors play an important role in promoting or delaying its development. The identification of susceptibility genes and genetic variants for obesity requires various methodological approaches. Obesity is classified into three main categories on the basis of genetic etiology: monogenic, syndromic, and polygenic obesity. Here we review monogenic and syndromic obesity. We also review the linkage analysis studies followed by the candidate gene approaches and genome-wide association studies. Identification of the underlying genetic causes of obesity will likely provide a basis both for the development of new therapeutic agents and for the personalized prevention of this condition. Received 2 October 2007; received after revision 15 November 2007; accepted 19 November 2007     

Heritable trinucleotide repeats and neurological disorders

In the past 3 years, seven human neurological disorders have been found to be associated with an abnormal number of unstable trinucleotide repeats within exons or non-expressed regions of a gene. These forms of mutations are called dynamic mutations. The expansion in copy number of trinucleotide repeats may represent a large number of hereditary disorders. The correlation between the length of the repeated size and the disease severity and variable onset has provided some genetic explanation for a phenomenon called anticipation. However, there are numerous questions which cannot be explained by anticipation. Many other factors such as genomic imprinting and variable DNA methylation may also contribute to the puzzling features of these phenotypes.     

The inherited susceptibility to cancer

The study of inherited cancer syndromes has led to the identification of over 25 genes directly involved in tumorigenesis. These genes have functions as diverse as signal transduction, cell cycle control, cell-to-cell adhesion, control of apoptosis, DNA repair and the maintenance of genome stability. Most cancer syndromes have a dominant pattern of inheritance, due to germline loss-of-function mutation of a tumour suppressor gene. All the recessively inherited genes have been implicated in the maintenance of genome stability. This review summarises our current understanding of the functions of the major cancer susceptibility genes.     

The complement system in age-related macular degeneration

Age-related macular degeneration (AMD) is a chronic and progressive degenerative disease of the retina, which culminates in blindness and affects mainly the elderly population. AMD pathogenesis and pathophysiology are incredibly complex due to the structural and cellular complexity of the retina, and the variety of risk factors and molecular mechanisms that contribute to disease onset and progression. AMD is driven by a combination of genetic predisposition, natural ageing changes and lifestyle factors, such as smoking or nutritional intake. The mechanism by which these risk factors interact and converge towards AMD are not fully understood and therefore drug discovery is challenging, where no therapeutic attempt has been fully effective thus far. Genetic and molecular studies have identified the complement system as an important player in AMD. Indeed, many of the genetic risk variants cluster in genes of the alternative pathway of the complement system and complement activation products are elevated in AMD patients. Nevertheless, attempts in treating AMD via complement regulators have not yet been successful, suggesting a level of complexity that could not be predicted only from a genetic point of view. In this review, we will explore the role of complement system in AMD development and in the main molecular and cellular features of AMD, including complement activation itself, inflammation, ECM stability, energy metabolism and oxidative stress.