Method: We employed a nested case–control study design. Psychiatric reference data were
available for 38500 patients attending a hospital-based psychiatric outpatient department
between 1998 and 2005. We enrolled 100 patients with delusional disorder and 50 patients
with paranoid schizophrenia as the subject cases, using DSM-IV criteria. We considered
equivalent numbers of healthy volunteers matched for age and ethnic background as
control subjects. All subjects came from an India-born Bengali population. We applied the
polymerase chain reaction–based molecular typing method to all patients and healthy
subjects.