In response to tdol, I guess it all depends upon where the OP lives.
I received a jury summons earlier this year, and it lists various reasons for which you can receive a deferrment. True, it's not the same as being totally excused from jury duty, but in the US, it might as well be, because you probably won't be summoned again for several years.

I have Lupus and was able to provide a doctor's note to defer me from jury duty. I've only ever been summoned one other time, and that was back in 1981, so that gives you an idea of the time lapses in the US jury pool.
However, I reiterate - follow the instructions of your summons to the letter. Mine specified that you cannot phone or email your request; it had to be in writing either by mail or by fax.