Is there a happiness gene?

It seems like with most things genetics is proving more complicated than the scientists anticipated:

The Corner on National Review Online

Media outlets will often speak loosely of things such as a “happiness gene,” a “gay gene,” or a “smart gene.” The state-of-the-art method for finding such a link is something called a “genome-wide association study” (GWAS). In a GWAS, scientists use blood or saliva samples to sequence the DNA for a group of several thousand people who exhibit a trait or behavior of interest (the “case group”), and for a second group of several thousand who do not exhibit the trait or behavior (the “control group”). Scientists then look for genetic differences between the two groups. In cases where a single malfunctioning gene creates, for example, a catastrophic disease that overwhelms other genetic and environmental factors, a GWAS can quickly pinpoint the culprit. Sometimes, however, the behavior or trait is caused by several interacting genes — so that, for example, Gene 1 has some effect only if Gene 2 has a special structure. This is called “epistatic interaction,” and can involve a large number of genes. Epistatic interactions make genetic effects harder to identify. Scientists deal with this problem and others by creating larger and larger case and control groups. The scaling up of such studies is among the most exciting frontiers in genetics. It is essentially an engineering problem, and money poured into solving it will likely improve human health through genetic screening and, ultimately, therapies.