They note that researchers often assume that those thousands of weakly-acting genetic variants will all cluster together in relevant genes. For example, you might expect that height-associated variants will affect genes that control the growth of bones. Similarly, schizophrenia-associated variants might affect genes that are involved in the nervous system. “There’s been this notion that for every gene that’s involved in a trait, there’d be a story connecting that gene to the trait,” says Pritchard. And he thinks that’s only partly true.
Yes, he says, there will be “core genes” that follow this pattern. They will affect traits in ways that make biological sense. But genes don’t work in isolation. They influence each other in large networks, so that “if a variant changes any one gene, it could change an entire gene network,” says Boyle. He believes that these networks are so thoroughly interconnected that every gene is just a few degrees of separation away from every other. Which means that changes in basically any gene will ripple inwards to affect the core genes for a particular trait. [...]
Pritchard’s team re-analyzed the GIANT data and calculated that there are probably more than 100,000 variants that affect our height, and most of these shift it by just a seventh of a millimeter. They’re so minuscule in their effects that it’s hard to tell them apart from statistical noise, which is why geneticists typically ignore them. And yet, Pritchard’s team noted that many of these weak signals cropped up consistently across different studies, which suggests that they are real results. And since these variants are spread evenly across the entire genome, they implicate a “substantial fraction of all genes,” Pritchard says. [...]
If Pritchard is right, it has big implications for genetics as a field. Geneticists are running ever-bigger and more expensive searches to identify the variants behind all kinds of traits and diseases, in the specific hope that their results will tell them something biologically interesting. They could show us more about how our bodies develop, for example, or point to new approaches for treating disease. But if Pritchard is right, then most variants will not provide such leads because they exert their influence in incidental ways.
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