What is the weight of genetics in preventing disease

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Is there any research or study which is to estimate the weight of genetics in preventing one or more diseases compared to other factors? A lot of time, for example, explaining how a particular kind of cancer occurs in someone, genetics is often mentioned, in addition to other factors, but how important (weight) is this factor among the others, in most cases it's not mentioned.

Maybe it's not known? Maybe the doctors consciously know that it's just too important so they don't want to discourage the public from doing something else to "fight against" genetics?

jim mcnamara

There is a lot of research on genetics and disease. A long time ago I taught a class on Medical Genetics. Back then it was clear there were many diseases known that had genetic component. An example: Conditions which involved damage to chromosomes or cause failure of chromosomes to "behave" during meiosis - creation of egg or sperm from one half of the chromosomes pairs in the parent. This one topic is related to multiple diseases, a few examples: trisomy 21, 15-21 translocation, and Cri du Chat Syndrome. There were other diseases mentioned and also more topics, back then.

The textbook was Thompson and Thompson 'Medial Genetics'. If I remember there were about 140 pages in the text. About 20 pages were dedicated to what I mentioned above, I think. So that was 1975. Lots of genetic involvement, right?

Wrong. https://www.amazon.com/dp/1437706967/?tag=pfamazon01-20
This is the 8th Edition from 2015. Lots of contributors. Well over 1000 pages, I believe. A monster compared to what we knew in 1975.

So, to be blunt, your question has not just a simple, yes answer: 'Genetics are involved in many diseases' It is incredibly more complex than you can imagine.
And we do not know all of the answers. One of our active posters is @Ygggdrasil who knows far more about this topic than I do. He may have good information for you.

15-21 is one of the Robertsonian genetic disorders:

Trisomy 21 an extra number 21 chromosome is an example

Cri du Chat Syndrome
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The contribution of genetics to human disease can range from 0% to 100%. There are examples of diseases that are basically 100% genetic; if you carry the gene for the disease, you will have the disease. Jim has listed some examples. There are also examples of disease that have almost no genetic component. For example, many infectious diseases—like HIV, influenza, and chicken pox—are caused by pathogens from the environment.

Of course, not everything in biology is so simple. The environment can change how genes are expressed and genes can affect how we respond to the environment, creating many cases in the middle. For example, some purely genetic diseases can be ameliorated by changes to an individual's environment. For example, phenylketonuria (PKU) is a genetic disease characterized by the lack of an enzyme needed to metabolize the amino acid phenylalanine. PKU can lead to neurological problems, but these neurological effects can be avoided if the individual avoids eating foods with high levels of phenylalanine. Genetics can also influence diseases caused by environmental factors like pathogens; for example, some individuals contain mutations that give them resistance to infection by viruses like HIV.

There are a wide variety of diseases and disorders—cancer, Alzheimer's disease, cardiovascular disease, autism, partisanship, etc.—that have some genetic component and some environmental component. To estimate the relative contributions of genetics to these diseases, researchers will rely on a number of different types of studies. One type of study involves looking at the rates of the disease in identical (monozygotic, MZ) versus fraternal (dizygotic, DZ) twins. Twins are generally raised in similar environments, but MZ twins will share 100% of their DNA while DZ twins only share 50% of their DNA. Researchers will look at the rate in which the twins are concordant for the disease; that is, whether they both have the disease or both do not have the disease. If the rate of concordance is higher in MZ twins than DZ twins, then the disease has a genetic component, and the difference in the rate of concordance between MZ and DZ twins can allow researchers to estimate roughly how much genetics contributes to the disease.

To identify genes that contribute to specific diseases, researchers can perform genome-wide association studies, in which they identify people with a particular disease and a similar group of people who lack the disease. They can then compare the DNA of the two populations to identify genetic markers associated with the disease. Follow up studies can then identify the genes near those markers and determine how they contribute to the specific disease.

Further reading (aimed at a general audience): https://ghr.nlm.nih.gov/primer/inheritance/heritability
For a comprehensive, technical discussion of the topic, see: https://www.nature.com/articles/nrg3377
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Long before DNA testing, I vaguely remember being quizzed by a geneticist about why my young brother and I seemed to be free of the auto-immune issues that beset the majority of my cousins. Thyroid, diabetes, arthritis etc etc. Seems 'we'd chosen our maternal grandmother well', inherited enough genetic traits to trump the potent HLA-group from other side of family...

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