Childhood risk factors

There is now a wealth of evidence attesting to the fact that a proportion of individuals who later manifest schizophrenia show abnormalities in their early development. The evidence for early developmental abnormalities in schizophrenia come from three main sorts of study:

• high-risk studies in which the offspring of parent(s) with schizophrenia are examined

• follow-back studies where cases of schizophrenia are ascertained, and their early developmental trajectory plotted with the help of history from the individual and family, sometimes also including such evidence as school reports, etc.

• cohort studies, where birth cohorts are followed up prospectively, and individuals who later manifest schizophrenia are compared with the rest of the cohort in terms of their early development.

High-risk studies

Studies of the offspring of schizophrenic mothers, the so-called 'high-risk studies', show that around 25 to 50 per cent show some deviation from normal in terms of their early development (reviewed by Davies et al.(32)). In the neonatal period there is a tendency to hypotonia and decreased cuddliness, in infancy milestones are delayed, in early childhood there is poor motor co-ordination, and in later childhood there are deficits in attention and information processing. Fish et al.(33) followed their cohort of 12 high-risk infants into adulthood. One developed schizophrenia and six showed schizotypal or paranoid personality traits; these authors coined the term 'pandysmaturation' to describe the abnormalities which included delayed motor milestones in the first 2 years of life.

Follow-back studies

High-risk studies have been criticised on the basis that they are unrepresentative because only a minority of people who develop schizophrenia have a mother with the same illness. Therefore researchers have carried out studies of reprentative groups of schizophrenic patients which relied on maternal recall to document the early development of adults with schizophrenia; these have shown impairment of cognitive and neuromotor development and interpersonal problems. These findings are more commonly reported in males than females, and tend to be associated with an early onset of illness. kf" The findings are not specific to schizophrenia, being reported also in the early development of some children who later manifest an affective psychosis. ^ Of course, one of the major criticisms of follow-back studies is the likelihood of recall bias. Studies that have avoided this problem include those which have accessed IQ scores assessed prior to illness onset; these have shown that premorbid IQ is, on average, lower in those, particularly males, who later manifest schizophrenia. (3 ^

Another source has been childhood home videos, which have been reviewed by researchers 'blind' to whether the individual later manifested schizophrenia. (38) In comparison with their healthy siblings, the preschizophrenic children showed higher rates of neuromotor abnormalities (predominantly left-sided) and overall poorer motor skills; the group differences were significant only at age 2 years.

Cohort studies

The publication of a number of cohort studies has overcome many of the criticisms of follow-back studies. In an investigation of the 1958 British Perinatal Mortality cohort, comprising 98 per cent of all children (n = 15 398) born in the United Kingdom in a certain week in March 1958, Done et al/39 compared those who later manifested schizophrenia (n = 40), affective psychosis (n = 35), and neurotic illness (n = 79) with each other as well as with 1914 randomly selected individuals with no history of mental illness. At age 7 years, teacher ratings showed the preschizophrenic children to have exhibited more social maladjustment than controls; the effect was most marked in boys. The preaffective children differed little from normal controls, whilst the preneurotic children (expressly girls) showed some maladjustment (over- and under-reaction) at age 11 years.

In a similar study of the 1946 British Birth Cohort, Jones et al.(40) determined that 30 out of 4746 individuals had, in adulthood, developed schizophrenia. This group were more likely than the rest of the cohort to show delayed milestones and speech problems, to have a lower premorbid IQ and lower education test scores at ages 8, 11, and 15 years, and to prefer solitary play at ages 4 and 6 years.

Together, such studies provide compelling evidence for a tendency of individuals with schizophrenia to show abnormalities in development which antedate the onset of illness. The findings are compatible with the notion that subtle brain abnormalities (which may be genetically or environmentally mediated, or both) underpin schizophrenia. However, it is also possible that some of the childhood risk factors are independent and act in an additive manner to set individuals on an increasingly deviant trajectory towards schizophrenia. Further information about epidemiological studies linking premorbid impairments and schizophrenia is given in Chapter 4.3.4.

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