This issue features groups of papers on genetics, the distributional nature of the milder disorder featuring most prominently in community surveys, diagnostic co-morbidity, neuropsychological and related aspects of schizophrenia.

The first group of papers come from genetic epidemiology, all from twin studies. Agrawal et al. (pp. 1155–1164) examine genetic and environmental origins of detailed aspects of social support. They find evidence for genetic elements in almost all aspects, with some smaller differences between males and females. Wichers et al. (pp. 1165–1174) report effects of pregnancy and birth complications and genetic elements on childhood behaviour problems. They find one specific complication, being of lower birth weight for gestational age, associated with problem behaviour, and an interaction with genetic effects, such that these are weaker in the presence of low birth weight. Johnson et al. (pp. 1175–1185) examine the heritability of depression measured on a symptom scale in Danish twins. They find genetic effects, which do not vary with age over a wide span from 45 to over 95. An accompanying editorial (pp. 1145–1148) looks at the future of genetic epidemiology in a time of accelerating molecular genetic research activity.

Epidemiological surveys frequently measure so-called common mental disorder, psychiatric symptoms in a milder range which may not necessarily fit defined criteria for specific disorders. Melzer et al. (pp. 1195–1201) using this kind of data from a community survey, find a continuous single distribution with no natural cut-off point. Brugha (pp. 1149–1154) in an accompanying editorial discusses the implications of such a dimensional approach and its relation to diagnosis.