Judges who learned that a convicted assailant was genetically predisposed to violence imposed lighter sentences in a hypothetical case than they otherwise would have, researchers reported on Thursday, in the most rigorous study to date of how behavioral biology can sway judicial decisions.... Defense lawyers now commonly introduce brain scans of convicted clients as mitigating evidence in appeals of death sentences, experts said.
How in the world is "my brain made me do it" an excuse?! Obviously any difference in our cognitive dispositions (including, say, an immoral indifference towards others' suffering) will be reflected in our brains somehow. And learning that this difference has a partly genetic cause certainly shouldn't make any moral difference. ("No, your honour, he didn't have a traumatic childhood; he was born that way! Isn't that so much better?")
Really the only consistent positions to hold when it comes to the question of moral responsibility are that either (i) no-one is responsible, due to the impossibility of pure self-creation, or else (ii) bad people should be punished, regardless of how they got to be that way. In neither case is genetics relevant. (Brain scans may be, on the second view, if they can show the harmful behaviour to due to mere temporary insanity or the like, rather than a lack of good will on the part of the agent.)