That goes back to my position that if a person were genetically predisposed to sin that would take choice and accountability out of the equation. If you can blame it on genetics you have a ready made excuse for the poor choices you make.
We have to keep in mind that regardless of our chemical makeup, derived from genetic variability or even prenatal nutrition and toxin exposure, we all end up in a physical form that is according to eternal plan and order. I don't believe that any mental or emotional deficiencies in a person would not have been planned for or even designed by that premortal spirit and the Lord. Even if we don't always understand the variations of choice and accountability, we have to trust that every person will be judged according to the Lord's perfect knowledge of our hearts and minds. It can definitely be a mystery why the Lord would allow trials that seem to undermine a person's agency, but there must be a purpose in it. All things are done in order and the plan is perfect, even if the path is not.