If a brain tumor turns you into a pedophile, are you any less culpable for molesting your stepchild?

I was reading an article in Slate.com which contained the following story:

“Mr. Oft,” a man who developed an interest in child pornography in middle age and then molested his stepdaughter. It turned out that Mr. Oft, a pseudonym, had a brain tumor. When the tumor was removed, his urges subsided; when it grew back, they returned.

Clearly, the tumor is strongly related to the behavior, but does that make Mr. Oft any less responsibile for his actions?

But please think about this more widely. If there is a physical structure or a unique chemistry in our brains that cause us to behave in specific ways, some of which may be anti-social or criminal, and others may be just weird, are we still responsible for our behavior?