My husband and I, along with our parents, are heavy. Is this a hereditary or genetic problem?
Undoubtedly, an element of genetic inheritance is involved in excess weight. In fact, two syndromes are clearly genetic: Bardet-Biedl syndrome and PraderWilli syndrome (discussed below). However, given the enormous increase in obesity in the last 20 to 40 years, it is clear that this is not due to “genetics” alone, since genes do not change that quickly. External environmental factors play a role. As some have said, your genes are not always your fate.
Bardet-Biedl syndrome
A rare familial, recessively transmitted genetic disorder. The clinical characteristics of this syndrome include impaired vision or even blindness, extra fingers, a diminished or missing sense of smell, disease of the heart muscle, abnormalities with the reproductive and urinary systems, mental and developmental abnormalities, and obesity.
Prader-Willi syndrome
A rare genetic disorder affecting one or more genes on chromosome 15. It is characterized by a difficult birth, poorly developed sex organs in the baby, failure to thrive, excess sleeping, speech delay, overeating and obesity, spine curvature, poor muscle tone, learning disabilities, and other abnormalities. The overeating may be extremely excessive, leading to morbid obesity.
The U.S. Office of Health Genomics (a part of the Department of Health and Human Services) has reviewed the effect of genes on excess weight. Evidence for a genetic basis of obesity includes studies of twins, as well as of very obese people who have mutations of single genes. The number of people who have an identifiable genetic problem, however, seems to be under 5% of people with excess weight.
Genes
Units of DNA within a chromosome that can produce a protein having a particular function or producing a change in the body.
Mutations
Permanent changes in genes. May or may not produce changes in the individual.
Leptin
A hormone produced by fat cells that seems to play a role in the appetite center of the brain.
Chromosome
Thread-like structures containing genes found in the DNA of a cell. There are 23 pairs of chromosomes in human cells.
Protein
One of the three main sources of energy for the body. Proteins are also prime building blocks for many of the cells in the body as well as for hormones, antibodies, enzymes, and other key compounds. One gram of protein contains four calories.
Nonetheless, with the mapping of human genes, a Human Genome Obesity Map has been developed and is progressing rapidly. The Office of Health Genomics cites single mutations in 11 genes. These were strongly implicated in 176 cases of obesity. Fifty chromosomal locations relating to obesity have been mapped, and genes that might play a role in obesity have been identified: 426 variants of 127 genes have been associated with obesity. A gene that causes a deficiency of leptin has been found; this deficiency leads to obesity, but is quite rare.
Thus, obesity and genetics are clearly related, and it is likely that, over the years, researchers will identify more genes that are associated with obesity. For many or most cases of obesity, there are complex interactions among multiple genes that affect weight and obesity. It is possible that genomic therapy will ultimately be developed to allow control of the “offending” genes in obesity as well as in many other medical diseases where research is actively underway.
It has recently been reported that a gene on chromosome 16 called the “fat mass and obesity-associated gene” might be responsible for up to 22% of all cases of common obesity in the general population. It is not yet known what the protein that this gene produces (transcribes) actually does, but it has been found that certain variants are associated with increased weight. There is also some link between this gene and diabetes and other components of the metabolic syndrome.
Bardet-Biedl syndrome: This is a rare familial, recessively transmitted genetic disorder. The clinical characteristics of this syndrome include impaired vision or even blindness, extra fingers, a diminished or missing sense of smell, disease of the heart muscle, abnormalities with the reproductive and urinary systems, mental and developmental abnormalities, and obesity.
Genetic disorder
A disease or abnormality in the body due to a problem in the DNA (gene, chromosome) of a person or organism that is inherited.
Hypogonadism
Poorly developed or incomplete sexual organs.
Prader-Willi syndrome: This rare genetic disorder affects one or more genes on chromosome 15. It is characterized by a difficult birth, poorly developed sex organs in the baby (hypogonadism), failure to thrive, excess sleeping, speech delay, overeating and obesity, spine curvature, poor muscle tone, learning disabilities, and other abnormalities. The overeating may be extremely excessive, leading to morbid obesity, which is perhaps the most troublesome part of the syndrome.
The “thrifty gene” hypothesis has been developed as a result of this work in genetics. This postulates that in ancient times humans developed genes to store fat so that during times of famine (when hunting or crops failed) the body would have a reserve of energy in the form of fat to get them through these tough times.
But now, in the Western world at least, where food is plentiful and we have become much more sedentary, we don’t need to store body fat for hard times. Thus, fat storage genes are a remnant of older times that are no longer needed. Yet, although everybody has these genes and cells, not everybody becomes obese. There are clearly other factors in play.