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Physical inactivity poses a major risk for obesity and chronic disease, and is influenced by both genetic and environmental factors. However, the genetic association between physical activity (PA) level and obesity is not well characterized. Our aims were to: (i) estimate the extent of additive genetic influences on physical activity while adjusting for household effects; and (ii) determine whether physical activity and adiposity measures share common genetic effects.
The sample included 521 (42 % male) adult relatives, 18–86 years of age, from five large families in the Southwest Ohio Family Study.
Sport, leisure and work PA were self-reported (Baecke Questionnaire of Habitual Physical Activity). Total body and trunk adiposity, including percentage body fat (%BF), were measured using dual-energy X-ray absorptiometry. Abdominal visceral and subcutaneous adipose tissue mass were measured using MRI.
Heritabilities for adiposity and PA traits, and the genetic, household and environmental correlations among them, were estimated using maximum likelihood variance components methods. Significant genetic effects (P < 0·05) were found for sport (h2 = 0·26) and leisure PA (h2 = 0·17). Significant (P < 0·05) household effects existed for leisure PA (c2 = 0·25). Sport PA had a negative genetic correlation with central adiposity measurements adjusted for height (ρG > |−0·40|). Sport and leisure PA had negative genetic correlations with %BF (ρG > |−0·46|).
The results suggest that the association of sport and leisure PA with lower adiposity is due, in part, to a common genetic inheritance of both reduced adiposity and the predisposition to engage in more physical activity.
Nutrigenomics is the study of how constituents of the diet interact with genes, and their products, to alter phenotype and, conversely, how genes and their products metabolise these constituents into nutrients, antinutrients, and bioactive compounds. Results from molecular and genetic epidemiological studies indicate that dietary unbalance can alter gene–nutrient interactions in ways that increase the risk of developing chronic disease. The interplay of human genetic variation and environmental factors will make identifying causative genes and nutrients a formidable, but not intractable, challenge. We provide specific recommendations for how to best meet this challenge and discuss the need for new methodologies and the use of comprehensive analyses of nutrient–genotype interactions involving large and diverse populations. The objective of the present paper is to stimulate discourse and collaboration among nutrigenomic researchers and stakeholders, a process that will lead to an increase in global health and wellness by reducing health disparities in developed and developing countries.
This chapter provides an overview of the methods currently available to study the genetic epidemiology of normal human growth and development. Over the past two decades numerous technological innovations have enabled researchers to investigate issues that were here to fore intractable. These innovations include the advent of relatively low-cost yet powerful computers, the development of sophisticated statistical genetic modelling approaches, and advances in high-throughput genotyping. Progress in these areas has allowed for more through genetic investigations of complex traits such as those comprising growth and development. These investigations not only assess the degree of genetic control of a trait, but also identify genes influencing variation in them.
A number of general points can be made regarding past research on the inheritance of growth-related traits. First, almost all studies to date have established that human growth is at least partly influenced by genes. These studies have examined familial resemblance of various growth and development measures including stature, weight and various maturational indicators (e.g. age at menarche, pubertal stage or skeletal age). Estimates of the proportion of variance attributable to the effects of genes (i.e. heritability) vary according to the trait of interest. Stature is among the most highly heritable of growth measures with estimates ranging as high as 0.92, indicating that as much as 92% of the total variation in stature can be attributable to the effects of genes (Wilson, 1976; Kaur and Singh, 1981).
Tay-Sachs disease (TSD) is the best known of the sphingolipidoses, a group of genetic disorders that includes Niemann-Pick disease, Gaucher’s disease, and others. Specifically, TSD is GM2 (beta) gangliosidosis, an autosomal recessive disease with complete penetrance. Affected individuals (recessive homozygotes) produce virtually no functional hexosaminidase A (hex A), an enzyme necessary for normal neurological development and function. TSD is very rare in most populations, but is, overall, about 100 times more prevalent among Ashkenazi Jews. This indicates that the TSD gene frequency is about 10 times higher in the Ashkenazi Jewish population. Persons with the disease usually show clinical symptoms of neurological degeneration by 6 months of age. Their condition steadily deteriorates, and they seldom live beyond the age of 4 years. There is no cure, but heterozygous “carriers” of the defective gene can be identified by clinical test, and amniocentesis can detect an affected fetus.
The British ophthalmologist Warren Tay (1881) first reported some of the early clinical signs of TSD. In the United States, Bernard Sachs (1887) further documented the clinical course and pathology of the disease he later called “amaurotic family idiocy” (Sachs 1896). 1896). It was Sachs who first noted the familial nature of the disease, and its seemingly exclusive occurrence in Jewish families. However, reports were soon made of non-Jewish cases. D. Slome (1933) was the first to survey the literature on the population characteristics of TSD and confirmed the disease’s autosomal recessive mode of transmission as well as the TSD gene’s higher frequency among Jews.
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