Monday, March 3, 2008

Genetics and Disease








Aaron Blaisdell said...

I decided to go back and read some of your early posts, starting at the beginning. Not sure if you'll ever see this comment, but here goes...

We can say that genes play a direct causal role in health, just as they play a direct causal role in just about every trait (morphological, physiological, behavioral). But the nature of the role they play is under debate. The fact that every human (except in extremely rate cases) is born with a four chambered heart, and bilaterally symmetrical, etc. These are traits that have genetic determinants (without having DNA these traits would not develop), but the heritability of these traits is zero. Thanks to Fischer for clarifying the distinction between "caused by genes" and a genetically heritable trait. Heritability is the amount of variance in a trait that has a genetic component. Thus, heritability is the real issue and is what the media should be focusing on. Of course, we all know that the media, in attempting to bring us the cliff notes version of science (and everything) dumbs it down to the point of oversimplicity and inaccuracy.

Stephan said...

Hi Aaron,

The first comment on this post! I basically see genetics (as it relates to idiopathic diseases) as determining your level of susceptibility to stressors.

For example, your HLA alleles determine how you react to gluten. But back in hunter-gatherer times, there was no gluten so it was moot.

trinkwasser said...

I'm doing the same thing, starting at the beginning and reading through.

I partly agree and partly disagree: for example one side of my family has a high proportion of sufferers from the consequences of insulin resistance up to and including Type 2 diabetes, the other does not - but they have an above average incidence of atypical depression.

Both sides of the family tend to die of cardiovascular disease, often at an advanced age, but almost no-one suffers cancer ever.

IME such familial disease patterns differing significantly from the population as a whole are far from uncommon, which suggests a genetic basis. The important bit is to determine what genes you may carry and how to NOT express them, which is where the environmental bit comes in.

Lacey said...


I think that is interesting about your family, but I don't think you got the point Stephan was trying to get across. To go back to the original Pima example: It does seem that the Pima are more susceptible to certain diseases, and that greater susceptibility would seem to be based on their genetic makeup. But are genetics the cause? Reread the original post.

nessuno said...

Genetics versus lifestyle. I often muse myself about the role of these two in determining one’s health history/prospects. You, Stephen, are inclined to accuse lifestyle in the first place for our illnesses. Don’t you think however, that genes themselves are also susceptible of degeneration? The fact is that some people living on a 100% western diet, with all the worse the term might involve, manage to avoid major health problems all their life long, some others, in spite of taking care of themselves, don’t. In my view, the pitfall of this thing with healthy lifestyle is just there: the effects don’t necessarily manifest themselves in the person who is abusing his health (or simply is ignorant, as more often the case is), but it will deteriorate the genes of his/her posterity. That is the reason why western nations (geography is increasingly losing its proper meaning in this context) are becoming sicker and sicker with every successive generation, I reckon. I would cite but one example: some African people living in western countries and eating the worst type of modern food still have healthy teeth. I suppose Europeans got their genes deteriorate over time as they have been longer on western diet. I don’t know if you follow me and see where I want to get. I just think, that genetic and lifestyle factors cannot be fully separated, because lifestyle can influence hereditary properties in the long run.

nessuno said...

Dear Stephan,

I have just realized that I have misspelt your name. I beg your pardon for that. I am a regular reader of your site; you helped me to understand some basic facts about nutrition.
May be you’ll find my previous comment a bit naïve, or lacking insight. As a matter of fact, I know very little about genetics. Maybe genes don’t change so quickly as to be responsible for the deterioration of health from generation to generation. But what is responsible than? If you keep a population on an un-altered bad quality diet for generations, will their general health stabilize itself on a certain (low) level, or will it get worse and worse? Now, if overall health of modern populations is declining, I can see but two possible explanations: either the quality of our foodstuffs is getting worse and worse, or the pernicious effects of a more or less unaltered diet are passed on to successive generations and thus getting accumulated in our genes. But again, I repeat, I don’t know much about genetics. Can some corporal defects be passed over to one’s progeny in some way other than via genes? For example let us take a couple suffering from deficiency of vitamin D, and having skeletal problems for this reason. Will they pass this illness on to their son? If yes, are the genes intact? As you can see, I am really a newbie in genetics. Your readers are quite enlightened, maybe doctors themselves, so you might find no interest in answering my questions.