Genetic linkage studies

Genotypes, obesity and type 2 diabetes – can genetic information motivate weight loss? A review

The current worldwide prevalence of type 2 diabetes (T2D) was estimated to be 2.8% in 2000, but it is predicted to increase to epidemic proportions in the coming decades, primarily due to lifestyle changes, particularly obesity. In the United Kingdom there are over 1.4 million men and women with T2D. In addition to a strong environmental element, the existence of an underlying genetic component to T2D risk is supported by twin studies, family studies and the widely different T2D prevalence across ethnic groups. Here we review data showing that several common genetic risk variants for T2D have now been successfully identified, with modest, but meta-analytical robust effects on risk (in the region of 1.1-1.5-fold risk per allele). Use of these in combination may have clinical utility in identifying subjects at high risk. Whether this information will be motivating to make the type of lifestyle changes that have been shown to reduce the rate of progression from the pre-diabetes state to overt T2D is discussed.

Genomics and complex liver disease: Challenges and opportunities

The concept of genetic susceptibility in the contribution to human disease is not new. What is new is the emerging ability of the field of genomics to detect, assess, and interpret genetic variation in the study of susceptibility to development of disease. Deciphering the human genome sequence and the publication of the human haplotype map are key elements of this effort. However, we are only beginning to understand the contribution of genetic predisposition to complex liver disease through its interaction with environmental risk factors. In the coming decade, we anticipate the development of human studies to better dissect the genotype/phenotype relationship of complex liver diseases. This endeavor will require large, well-phenotyped patient populations of each disease of interest and proper study designs aimed at answering important questions of hepatic disease prognosis, pathogenesis, and treatment. Teamwork between patients, physicians, and genomics scientists can ensure that this opportunity leads to important biological discoveries and improved treatment of complex disease.

A direct assessment of genetic contribution to the incidence of coronary infarct in the general population Greek EPIC cohort

To estimate the fraction of the incidence of coronary infarct attributable to the combined action of common genetic polymorphisms likely to be related to this condition, we conducted a case-control study nested within the Greek component of the European Prospective Investigation into Cancer and Nutrition. A total of 202 cases with a new, medically confirmed coronary infarct and 197 controls who had not developed an infarct by the time the corresponding case was diagnosed, were identified. A simple a priori score, relying on a total of 11 genetic polymorphisms was developed. Each polymorphism contributed 1 unit if the subject was homozygous for the high-risk allele, 0.5 units if the subject was heterozygous and 0 units if the subject was homozygous for the low-risk allele. Cases were over-represented in the presumed high genetic risk score values (chi square for trend = 10.18; p = 0.0014). The odds ratio to develop coronary infarct was 1.55 (95% confidence interval: 1.02-2.37) for score > or = 3.0, and 2.02 (1.31-3.11) for score > or = 3.5. In both instances the population fraction of the disease attributable to genetic predisposition exceeded 22%. Assuming a prior probability of at least 0.10 for the score to be predictive of coronary infarct risk, our findings are more likely than not to be truly positive. Our results, based on a simple score integrating the additive impact of 11 genetic polymorphisms, indicate that genetic predisposition accounts for a considerable fraction of the incidence of coronary infarct in the community.

Genetic basis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a clinically heterogeneous condition with a complex aetiology in which environmental and genetic factors are implicated. The contribution of human leukocyte antigen (HLA) genes, particularly the HLA-DRB1 gene, to RA genetic predisposition was the first described, and remains as the best characterised single genetic risk factor contributing to RA. However, it has been estimated that only 30% of the genetic contribution to RA can be attributed to HLA genes and it is suggested that other non-HLA genes may play a relevant role in RA susceptibility. Linkage studies and association studies are the two main strategies used in the investigation of genetic factors contributing to complex genetic traits. In this work we review the progress made in the field of RA genetics, focusing mainly on the contribution of candidate gene association studies to the dissection of RA genetic risk factors.

Genetic susceptibility to infectious diseases: big is beautiful, but will bigger be even better?

Genetic epidemiology, including twin studies, provides robust evidence that genetic variation in human populations contributes to susceptibility to infectious disease. One of the major limitations of studies that attempt to identify the genes and mechanisms that underlie this susceptibility has been lack of power caused by small sample size. With the development of novel technologies, burgeoning information on the human genome, the HapMap project, and human genetic diversity, we are at the beginning of a new era in the study of the genetics of complex diseases. This review looks afresh at the epidemiological evidence that supports a role for genetics in susceptibility to infectious disease, examines the somewhat limited achievements to date, and discusses current advances in methodology and technology that will potentially lead to translational data in the future.

Host susceptibility to persistent hepatitis B virus infection

Genetic epidemiology researches such as twin studies, family-clustering of hepatitis B virus (HBV) infection studies and ethnic difference studies have provided the evidence that host genetic factors play an important role in determining the outcome of HBV infection. The opening questions include which human genes are important in infection and how to find them. Though a number of studies have sought genetic associations between HBV infection/persistence and gene polymorphisms, the candidate gene-based approach is clearly inadequate to fully explain the genetic basis of the disease. With the advent of new genetic markers and automated genotyping, genetic mapping can be conducted extremely rapid. This approach has been successful in some infectious diseases. Linkage analysis can find host genes susceptible to HBV and is of great clinical importance.