Pima Medical Institute

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Assiduous readers of newspaper science columns will remember the stream of announcements in the 1990s of the discovery of genes "for" everything from impulsive behavior to schizophrenia to heart disease and cancer. (Not to mention the so-called gay gene.) In the fine print, the authors of those studies made clear that they thought the genes they'd located made only small contributions to the condition in question. But even those limited effects failed to hold up in most cases. A recent literature review by Joel Hirschhorn, a geneticist at the Broad Institute in Boston, found that only six of the 166 initially reported associations of genes with a disease or trait had been replicated consistently. It may turn out that many inherited diseases aren't connected to genes at all. The genome project itself showed why this is so. Some geneticists guessed, based on the number of RNA transcripts discovered by the late 1990s, that there were as many as 150,000 genes in the human genome. Genomic companies like Incyte patented many of those transcripts. But the number of genes has proved to be closer to 20,000. A lot of the RNA transcripts, it turns out, play other roles in the cell - more available