What Conclusion Has Been Reached Regarding the Genetic Status of Schizophrenia

What conclusion has been reached regarding the genetic status of schizophrenia using genome-wide association studies?

A) A single dominant gene is involved.
B) No single gene or allele makes a significant contribution.
C) A single recessive gene is involved.
D) Several dominant genes located on the X chromosome cause this disease.
E) No more than three loci are involved in the expression of schizophrenia.