First, two large studies found two rare deletions that are significantly associated with schizophrenia, on chromesomes 1q21.1 (0.2% of cases) and 15q13.3 (0.3%). (55, 56) The case:control ratios (around 10) suggest major effects on risk, but it is unknown which deleted genes or sequences are responsible, or whether they account for all of the subject’s genetic risk. These deletions are also seen (but probably less frequently) in individuals with mental retardation and/or autism, and are typically de novo (not inherited from parents).(55) The well-known chromosome 22q11 deletions were also significantly associated with schizophrenia (0.2-0.4% of cases across studies vs. 0% of controls).
