A lot of the misunderstandings in the press and among the public about studies of genetic causes of disease could be solved by a single observation: The answer to the question “is that disease caused by genetics or environment?”, the answer is most always “both”. There are very few diseases such that particular genes are necessary (that is, people never gets the disease absent those genes) and sufficient (that is, everyone who has those genes gets the disease). Even if we appropriately weaken these condition some – e.g., calling it sufficient even though there are exceptions if people do not live long enough or have the vulnerable body parts removed – there are still very few. Huntington’s Disease is a well known exception, wherein a particular genetic pattern dooms someone, no matter their environmental exposures, unless they die from something else first.
There are a few health outcomes that can be considered entirely environmental (note that in this context, the term “environmental” refers to anything external that affects a body, including infectious agents, diet, etc., which is roughly the same as saying anything that is not genetic; it does not have anything to do with the “eco” sense of the word environment). Someone who is severely damaged by trauma or other major physical insult (plane crash, IED, engulfing fire) or severe chemical insult (getting no oxygen for a long period, ingesting a lot of poison) can be doomed from that environmental exposure. The particulars of his genetics do not matter, unless you really push the definitions to absurd levels (if it were not for his genetics, he would not have been a member of a tool-using species, so he never would have…). But even then, if someone is not killed immediately, chances are that genetic factors will affect whether he recovers.
Huntington’s and trauma are the exceptions. For most diseases, someone’s particular personal engineering (mostly genetic) and what they are exposed to in life both matter. With rare exceptions, studies of genetic causes of disease, just like studies of environmental cause, find that a particular pattern increases the risk, but very seldom is it 0% in the absence of the pattern/exposure, and even less often does it increase to 100% in the presence. Instead, the risk changes from something in between those two extremes to something else in between; the probability changes, but the particular factor does not fully explain the outcome. Other factors are also causal.
With that in mind, consider the recent studies that found some possible genetic explanations for some cases of autism, which were reported in the press, including good reports here and here. The new studies focused on genetic characteristics that are believed to be “spontaneous changes”. That is, they are not something that is passed down through families, the type of genetics we usually think about, but are things that happen to one person’s genes that may cause the outcome. (Note that I include the caveat “are believed” because despite the hype you read, the understanding of how physically inherited characteristics worth has enormous limitations. So it is possible that these genetic changes are pre-programmed by standard heredity, but in ways we do not yet understand. I wonder how many genetic epidemiology researchers actually understand that.)
The two news stories linked above were decent, though glaringly absent from the stories was a clear explanation that both genetics and environment are almost certainly a cause for most cases of all diseases. But anyone reading the articles with just that bit background knowledge would get a pretty good understanding of the appropriately modest claims. In particular the stories recognize that the more important genetic causes are inherited and unknown, presumably environmental, factors are more important still. The new studies and discoveries were largely basic science – that is, something that is a matter of curiosity that might prove important for some reason someday, but is definitely not where you would focus to answer applied science points about “why is there so much autism these days and what can we do about it?”
That brings up the question of whether these genetic changes are themselves environmental. The researchers are pretty sure that they come from changes the parents’ sperm or eggs, but are not so sure about why they happen. As the news stories mentioned and most readers know, autism incidence has increased dramatically over a few decades. Standard genetic factors – those that are passed on from one generation to the next – cannot explain a trend like this because our collective genes cannot change over the course of a generation or two. Indeed, with only a few very unusual exceptions, genetics have not really changed within recorded history. Only environmental changes can explain trending like this. The LA Times story (first link above) did not reach that level of sophistication in their explanation, but they did pursue the point. They talked to Irva Hertz-Picciotto, an expert on the subject (and someone who was once a friend and colleague and editor of a journal I was the editor of, though I have not talked to her in years, and who I believe is one of the genuinely good epidemiologic researchers). She pointed out that the obvious conclusion is that the changes may well have environmental causes.
All in all, this is an interesting discovery, though with limited immediate practical scope (the numbers presented mean that these genetic changes could explain at most a few percent of all autism cases), and a perfect example for a tutorial in genes and environment. Of course, this being about autism, there had to be political spinning.
The American Counsel on Science and Health, whose melange of political positions include attacking any claim that there really is an environmentally-caused upward trend in autism, commented on the study. They seemed to suggest that the new studies help vindicate their preferred position that there are no environmental causes of autism, and thus the apparent trend is all a change in diagnosis. (Certainly some of the trend is that, but it seems very unlikely that explains all of it.) They criticize Irva for being “intentionally vague” about her observation, perhaps not realizing that the soundbite quotes that end up in newspaper articles usually oversimplify what someone told the reporter, to put it charitably. Exactly what was she supposed to do?
But they do have a point that it may be that there is no time trend in these particular genetic changes since they account for, at most, a tiny portion of all autism. The environmental causes of the change in autism incidence might exist only within the vast majority of autism cases that are not currently attributed to genetics of any type. Still, the reader of their comment is likely to come away thinking they new results argue against the environmental explanation, which they clearly do not. This is a case where the readers of mass media health reporters will actually have gained greater understanding than those who read the critical analysis (for the specific pieces I link here, anyway). In a role reversal, the former did real somewhat in-depth analysis, and the latter put out confusing statements following what seems like an over-simplified script.