Obesity Genes & Twins
Obesity - Environmental Factors
Obesity is strongly influenced by environmental factors, the prevalence
of obesity increases so rapidly in many populations that the changes cannot
be attributed to changes in genetic inheritance. The degree of an individual's
obesity and body weight can be modified by interventions in energy intake
or energy expenditure.
Obesity - Genetics & Twins
There is no doubt however that obesity is also influenced by genetics.
That obesity runs in families is an old observation, and it has been repeatedly
confirmed in multiple studies in populations from different parts of the
world who have lived in different environments. Studies of monozygotic
and dizygotic twins have unambiguously shown that there is a much greater
resemblance in the degree of obesity and overweight between genetically
identical monozygotic twins; this indicates that the resemblance is related
to their similar genes rather than their shared environment. However,
these studies may have overestimated the effect of genetics if monozygotic
twins share exposure to more environmental effects than dizygotic twins
do. A study of 311 pairs of twins who had been raised apart and 362 pairs
who had been raised together indicated that the shared childhood environment
has little or no influence on obesity.
Abdominal Obesity & General Obesity
The pattern of inheritance of obesity strongly suggests that the effect
is polygenic, with each variant of many different genes making a small
difference in effect. As a phenotype obesity is also heterogeneous, and
there are at least two distinct but frequently overlapping subtypes: general
obesity, which results in increased body fat mass, and abdominal obesity.
The phenotypes seem to have some of the same genetic and environmental
influences in common.
Obesity Gene
Since the identification of the leptin gene, many other single genes have
also been investigated as candidates for causing obesity, and the entire
genome has been scanned for loci associated with obesity. A few genes
have been found to cause monogenic forms of obesity in humans. However,
there has been no convincing success in describing the polygenic background
of common obesity.
2001
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