My opinion is that we actually have many lives. And each life is to provide us with experiences that we need to fill the voids in our soul. Then being handicapped is perhaps a useful experience for one of our lives.
It seems, from observation of the condition of humanity on this planet, that pain and suffering are also needed experiences. Many experience pain and suffering all their lives. Most of us experience it near our death.
My father was an exception. After smoking and drinking, sometimes to excess all his life, he died peacefully in his sleep at age 96. So I think you are right about the importance of genetics.
Most of you out there are unlikely to buy the "many lives" explanation for conditions on earth, since western religion preaches that we only have one life. But I would like to point out that the idea of "one life" developed at the time that Christianity became a Roman state religion. It provided for more control of the masses if they thought there was only one life. If there were many, then the masses would be more likely to risk their lives against the authorities.
The Jews had a concept of many lives they called Transmigration, in which the soul, but not the consciousness, migrated to another body after death. Moses may have been referring to many lives when he discussed how many generations the guilt of various sins would last. That would essentially be the same as the concept of Karma in eastern religions if it were true. And since there is only one god, it probably is true.
Besides all that, I personally like the idea that the soul evolves, as well as the body, through cycles of life and death. But I hope that some form of consciousness is preserved. My guess is that it is preserved beyond death, but not beyond rebirth in a physical form, since most of us have no memory of previous lives.
Even if we progress enough to no longer require physical rebirth, my guess is that we will continue to cycle through life and death on higher spiritual levels with consciousness preserved until we become akin to god. Otherwise the soul would become complacent.