I'm not certain if you meant just a physical cause... or any possible root cause. I can provide a perspective for the latter, which may stretch your comfort level.
It is no secret that throughout history, we have numerous examples of people being not only aware of a past life but the influence it was having on the present one. Mozart was prodigy, writing incredible music at 6. He claimed that his musical talent was developed in another lifetime. Gen. Patton was also a firm believer in past lives, and expressed that openly in poems like Through a Glass Darkly. He rose to a very high rank and his military tactics are still taught to perspective officers. My point is that if it is possible to bring special skills or abilities into an incarnation, then there is potential to bring other, less desirable things as well.... like OCD.
Rather than try to explain its intricacies, I'll just leave a link that gives a great explanation. I'm not saying this is truth, but with the incredible complexity of the universe, their explanation does have some validity.