Is it necessary to distinguish between first and second generation African-Caribbean populaton in psychiatric research?

In attempting to identify factors responsible for the onset, course and prognosis of an illness, it is necessary to identify differences between generations in order to separate the effects of heritability and environment. Ethnicity and culture can also be examined in this way so that changes in culture occasioned by changes in environment can be assessed in terms of their impact on illness. In our work on the family history of psychoses among the African-Caribbean population in Britain we have found that for schrizophrenia, the relatives of first generation (those born in the Caribbean) and white psychotic patients share similiar risks while the risk is markedly increase in the relatives, particularly siblings of the second generation (those born in Britain to Caribbean parents) psychotic patients. For affective psychoses, we have found that the risk in the relatives of the first generation patients is significantly less than for both the white and the second generation relatives. These differences would have been much less noticeable if the separation between first and second generation patients had not been undertaken and would have been more difficult to interpret. Our findings do suggest that there are factors acting on the second generation making them more susceptible than their first generation counterparts to psychotic illness. This therefore diminishes the likelihood that the increased risk of illness in the second generation is due to a genetic effect and is much more likely to be mediated by some selective environmental effects acting either specifically on those families already afflicted by the disease or more generally on the entire second generation population.(AU)