Obesity is a complex multifactorial chronic disease
developing from interactive influences of
numerous factors—social, behavioral, physiological,
metabolic, cellular, and molecular. Genetic
influences are difficult to elucidate and identification
of the genes is not easily achieved in
familial or pedigree studies. Furthermore, whatever
the influence the genotype has on the etiology
of obesity, it is generally attenuated or exacerbated
by nongenetic factors.
A large number of twin, adoption, and family
studies have explored the level of heritability of
obesity; that is, the fraction of the population
variation in a trait (e.g., BMI) that can be
explained by genetic transmission. Recent studies
of individuals with a wide range of BMIs,
together with information obtained on their parents,
siblings, and spouses, suggest that about 25
to 40 percent of the individual differences in
body mass or body fat may depend on genetic
factors. 329-331 However, studies with identical
twins reared apart suggest that the genetic contribution
to BMI may be higher, i.e., about 70
percent. 332 There are several other studies of
monozygotic twins reared apart that yielded
remarkably consistent results. 333 Some of the
reasons behind the different results obtained
from twin versus family studies have been
reported. 334-336 The relative risk of obesity for
first-degree relatives of overweight, moderately obese, or severely obese persons in comparison
to the population prevalence of the condition reaches about 2 for overweight, 3 to 4 for moderate
obesity, and 5 and more for more severe
obesity.
Obesity is a complex multifactorial chronic diseasedeveloping from interactive influences ofnumerous factors—social, behavioral, physiological,metabolic, cellular, and molecular. Geneticinfluences are difficult to elucidate and identificationof the genes is not easily achieved infamilial or pedigree studies. Furthermore, whateverthe influence the genotype has on the etiologyof obesity, it is generally attenuated or exacerbatedby nongenetic factors.A large number of twin, adoption, and familystudies have explored the level of heritability ofobesity; that is, the fraction of the populationvariation in a trait (e.g., BMI) that can beexplained by genetic transmission. Recent studiesof individuals with a wide range of BMIs,together with information obtained on their parents,siblings, and spouses, suggest that about 25to 40 percent of the individual differences inbody mass or body fat may depend on geneticfactors. 329-331 However, studies with identicaltwins reared apart suggest that the genetic contributionto BMI may be higher, i.e., about 70percent. 332 There are several other studies ofmonozygotic twins reared apart that yieldedremarkably consistent results. 333 Some of thereasons behind the different results obtainedfrom twin versus family studies have beenreported. 334-336 The relative risk of obesity forfirst-degree relatives of overweight, moderately obese, or severely obese persons in comparisonto the population prevalence of the condition reaches about 2 for overweight, 3 to 4 for moderateobesity, and 5 and more for more severeobesity.
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