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Unity and diversity in schizophrenia.

Schizophrenia can be recognized reliably in very different parts of the world.' Recent cross-national, diagnostically blind studies of schizophrenia in twins from London2 and similarly blind assessments of interviews with the blood-relatives of schizophrenics who had been adopted in Copenhagen have helped both to validate the diagnosis and to confirm the importance of genetic factors in its aetiology.3 As Kety3 says, ifthe mental illness called schizophrenia is a myth,4 it is a myth with a strong genetic component. What is far from clear, however, is the extent to which schizophrenia is homogeneous or heterogeneous genetically and how the various forms of the disorder are related to conditions clinically similar to it. The spectrum of schizophrenic disorders ranges from the deteriorating chronic cases through the well-preserved paranoid and the good-prognosis schizoaffective to latent, borderline cases and socially well-functioning schizoid personalities; and it is reasonable to suggest that there is a genetic unity in the sense that all parts of it act in the same direction-increasing the likelihood of schizophrenic disorder in the offspring, though not necessarily to the same degree.5 Shields6 suggested that in moving from one end of the spectrum to the other the aetiology of the disorders becomes increasingly heterogeneous. The opposite hypothesis is that different clinical classifications and subtypes to a large extent reflect different aetiologies, some non-genetic, some more closely related to the group of affective disorders than to schizophrenia, and others distinct disease entities. Kleist and his pupil Leonhard proposed a complex classification within the schizophrenias based on end state. This has not so far received satisfactory genetic validation,7 and with improved treatment such subtle clinical distinctions become more difficult to draw. At the end of the last century Kraepelin grouped within the term dementia praecox three disorders which had previously been regarded as separate: hebephrenia, catatonia (first described by Kahlbaum 100 years ago), and dementia paranoides. Though presenting varied clinical pictures they had certain characteristic psychological symptoms in common and (compared with manic-depressive psychosis) a generally unfavourable outcome. Kraepelin was reluctant to speculate about the aetiology of what he observed. Bleuler's "group of the schizophrenias," which he described in 1911, referred to a class of patients only slightly wider than Kraepelin's-the plural reflected his uncertainty about the aetiological unity of the clinical group.8