Genetic studies have provided suggestive evidence for loci conferring susceptibility to schizophrenia on chromosomes 6p and 22q.The possible involvement of unstable DNA sequences (dynamic mutations) has also created interest. Studies of in-utero exposure to influenza epidemics as a risk factor have produced conflicting results. The evidence for a relationship between obstetric complications and schizophrenia has been strengthened, but its meaning remains unclear.