Scientists are eyeing a rare genetic glitch for clues to improved treatments for some people with schizophrenia — even though they found the mutation in only one third of 1 percent of patients. In the study, funded in part by the National Institutes of Health, schizophrenia patients were 14 times more likely than controls to harbor multiple copies of a gene on Chromosome 7. The mutations were in the gene for VIPR2, the receptor for vasoactive intestinal peptide (VIP) — a chemical messenger known to play a role in brain development. An examination of patients’ blood confirmed that they had overactive VIP activity.