Hungarian twin studies: Results of four decades
Semmelweis Egyetem, Általános Orvostudományi Kar Radiológiai és Onkoterápiás Klinika Budapest Üllői út 78/A 1082.Orvosi Hetilap 10/2013; 154(40):1579-1586. DOI: 10.1556/OH.2013.29707
Twin studies play a role in examining the contribution of genetic variations and environmental factors responsible for the determination of phenotypic variables and of genetic linkage between genotypes. Hungarian twin studies, supported by three twin registries (among them two twin-database), date back to 1970s. Studies mainly focused on various congenital abnormalities, the effect of contraceptive pills and folic acid on the frequency of twin pregnancies, as well as psychosexual and alcohol consumptional behaviors. Monogenic Mendelian inheritance of lactose (mal)absorption was demonstrated for the first time. Hungarian Twin Registry was founded in 2007, which contributed to the current understanding on the background of several disorders, e.g. metabolic syndrome and atherosclerosis. As part of an international twin study, among others, arterial stiffness, central blood pressure, carotid intima/media thickness, venous biomechanics, body composition, lung function and smoking characteristics were also assessed. Absence of genetic background in non-alcoholic fatty liver disease and high inheritance of carotid plaque characteristics were demonstrated for the first time. The review also aims to summarize future plans of the Hungarian Twin Registry. Orv. Hetil., 2013, 154, 1579-1586.
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ABSTRACT: Background Ultrasound measurements of renal dimensions are conventionally limited to renal length, shape and cortical thickness. These are regarded as adequate for normal therapeutic decision making and volume measurements are reserved for a few clinical trials. However, there is no evidence concerning the degree to which renal length or volume are independently susceptible to heritable and environmental influences. Aims: We aimed to determine whether renal length or width (as a surrogate of volume) were more influenced by heritability.MethodsA single operator measured renal length and width in 114 adult monozygotic and same-sex dizygotic Hungarian twin pairs (mean age 43.6±16.3 years), using an Esaote MyLab 70X ultrasound machine with curved array transducer (1–8 MHz, CA431).ResultsAnalysis of within-pair co-twin correlations adjusted for age and gender showed that the age- and sex-adjusted heritability of average renal length was 51% (95% confidence interval [CI], 29 to 72%). Renal width showed negligible genetic influence. Common environmental effects had no influence, and unshared environments were responsible for 49-80% of the variance, mainly renal width.Conclusions This study is the first to demonstrate the moderate heritability and limited environmental influence on renal length, and the contrasting lack of heritability of renal width, which is mainly influenced by unshared environmental components, i.e. lifestyle habits. Renal width therefore better represents the influence of modifiable environmental factors than renal length. The results suggest that renal width not length should be reported to facilitate early detection and monitoring of renal disease.
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ABSTRACT: The increasing burden of cardiovascular disorders highlights the crucial need to research efforts in the prevention and screening of heritable disorders or cardiovascular risk factors. Twin studies offer an opportunity to assess the influence of genetic and environmental factors and gene–environment interactions as well. Blood pressure and its components, arterial stiffness, carotid intima-media thickness were found to have a moderate heritability, whereas carotid plaque formation and coronary atherosclerosis seemed to be strongly genetically determined. These findings so far underlined the importance of identification of the specific genetic factors and prevention in high-risk individuals due to genetic transmission; therefore, further studies should investigate the benefits of a possible screening program. Beyond this “classical” model, monozygotic twin pairs discordant for a disease are important research opportunity since this method is able to assess the role of prenatal and postnatal environmental (epigenetic, stochastic) factors in the development of a disease. Longitudinal twin studies provide an ideal model to investigate the within-pair epigenetic drift (e.g. DNA methylation, histone modification) over time. In the future, these twin studies might unravel the underlying epigenetic changes associated with cardiovascular disease-risk biomarkers, which can help in the identification of those individuals who have higher risk for future cardiovascular disorders. Since in most twin studies a considerable role is found for unique environmental factors, the “traditional” concept of the deterministic role of individual-specific modifiable environmental factors, such as smoking, unhealthy nutrition or reduced physical activity, still remains important.
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ABSTRACT: Over the past few years, use of the genome-wide association study (GWAS) has made it possible to identify the primary genetic mechanisms of essential hypertension. GWAS results have helped identify many loci in or near genes that generally were not expected to be associated with blood pressure or essential hypertension. However, considering the great expectations of improving clinical outcomes and the billions of dollars that have been spent on various GWASs, the progress made so far has been slow. There are several factors that could be responsible for the relative lack of success of GWASs. First, it is possible that the number of people enrolled in the various GWASs was not enough, thereby limiting the power to detect additional markers. Second, although the alleles that are associated with a modest increase in risk are constantly being found, their discriminatory ability and use as predictive markers has been quite low. Difficulties with control group selection along with unrepeatability have also been problematic when using GWASs. The current paper summarizes the recent progress attained when using a GWAS of hypertension to identify the many loci associated with essential hypertension. In this review, we discuss the progress and issues of a GWAS for hypertension.
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