That is, only half of the people with the allele showed schizophrenic symptoms. Research seems to have stopped there. The next step of research should have been to study the families of the patients and non-patients to determine differences, if any, in their communication patterns. The results of that research would have made a further step, examination of the variability in chemical pathways involving the normal allele and the mutant allele, feasible and necessary. The money ran out, and it never happened.
Scientists love complexity, but funding agencies are often another matter.