Something like 3500 Mendelian (single gene) genetic diseases have been discovered but the vast majority of our genetic diseases appear to be multi-genic. Something like 90 genes are known to be associated with Schizophrenia. Some of these involve proteins that have functions that can be directly linked to the brain. Four of them code subunits of a calcium channel protein, that is, a protein involved in the flow of ions into and out of cells, known to be active in nerve cells.
Elucidating the exact way each of these contribute to disease will take a while, but diseases are not the only area where modern genomic statistical analysis will elucidate genetic influence. Height, running speed, and adult IQ are all other areas known or strongly suspected to be under the control of multiple genes. Genomic analysis has developed powerful tools for discovering the function of identified genes, and investigators have gotten rather good at designing customized mice. The designer human will almost certainly be within reach in one or at most two decades.
This will present a temptation that will be difficult to resist. In the first place parents will want offspring that don't have any of the obvious disease causing genes. Once you start tampering with the genome, can you deny your child a slightly more athletic build, a prettier face, or a few more IQ points?