Biological abnormalities in the relatives of schizophrenics

Relatives have been examined for some of the biological abnormalities which are found in their schizophrenic kin. Thus, in the Maudsley Family Study, Sharma et al.(1 16) carried out magnetic resonance imaging (MRI) scans on families with several members affected with schizophrenia. Both the schizophrenic members and those unaffected relatives who appeared to be transmitting the liability to the disorder (so-called obligate carriers) showed larger lateral ventricles than controls as well as loss of the normal cerebral asymmetry. This latter finding gives some support to Crow's (ID hypothesis that an abnormality in the genetic control of the development of normal asymmetry contributes to schizophrenia.

In the same Maudsley Family Study, the non-psychotic relatives exhibited other neurophysiological abnormalities such as an excess of delayed P300 event-related potentials; their prevalence was not as high as in the patients themselves but higher than in normal controls. (!9 Those patients who showed an excess of saccadic distractability errors tended to have relatives with the same eye-tracking abnormalities. (19) The schizophrenic patients and their well relatives from these multiply affected families also showed more integrative neurological abnormalities than controls. (20)

These findings suggest that what is being transmitted is not genes for schizophrenia per se but rather genes for a variety of characteristics (e.g. schizotypal personality, enlarged lateral ventricles, loss of cerebral asymmetry, delayed P300, integrative neurological abnormalities, etc.) which increase the risk of schizophrenia. Individuals can inherit these characteristics without being psychotic; perhaps schizophrenia only ensues when an individual inherits a number of such endophenotypic abnormalities and passes a critical threshold of risk. (21

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