Developmental aspects of schizophrenia and related disorders: possible implications for treatment

Schizophrenia and other schizophrenia-spectrum disorders are neurodevelopmental disorders which may share genetic susceptibility factors and represent differential expressions of an underlying vulnerability. Schizophrenia may have its onset in childhood and can be reliably diagnosed. However, developmental factors modulate disease expression in children.

Although the prevalence of schizophrenia in childhood is low, children who develop schizophrenia in adult life may show subtle and non-specific developmental abnormalities, consistent with the neurodevelopmental hypothesis.

Studies of the schizophrenia prodrome also demonstrate that abnormalities may be apparent years before the onset of positive symptoms. Such evidence raises the possibility of using preventive approaches in the treatment of schizophrenia. Further advances in our knowledge of the aetiopathology of schizophrenia (and the identification of endophenotypes within the group of schizophrenia and related disorders) may further improve our ability to predict disease development, making implementation of preventive interventions more achievable.

Schizophrenia and schizophrenia-spectrum disorders are neurodevelopmental in origin and are likely to represent differential expression of an underlying vulnerability. Children who develop schizophrenia in adult life may show non-specific developmental abnormalities. Moreover, studies of the schizophrenia prodrome show that abnormalities are observed years before the onset of positive symptoms. This article describes developmental aspects of schizophrenia and related disorders and the implications of these findings for assessment and early intervention.

Clinical features
Schizophrenia
Schizophrenia is a chronic psychiatric disorder, with a lifetime risk of about 1%. Its clinical features can be conceptualised in a number of ways. One of these is their broad division into positive and negative symptom clusters. Alternatively, the characteristic symptoms of schizophrenia can be divided into three syndromes or dimensions of illness (Liddle, 1987) as in Box 1Go: reality distortion (delusions and hallucinations); psychomotor poverty (negative symptoms); and disorganisation (thought disorder). In addition to the clinical symptoms, a range of neurocognitive abnormalities may be present and may be associated with functional outcome. These include deficits in attention, verbal memory, working memory and executive function. These deficits may be antecedents, rather than consequences, of the illness.

Most populations show similar prevalence rates of schizophrenia of between 1.4 and 4.6 per 1000. Incidence rates for the disorder are dependent on the diagnostic criteria used to ascertain caseness (Jablensky et al, 1992).

Schizotypy
Schizotypy (or schizotypal personality disorder), like schizophrenia, is syndromal in nature. The three main components of the syndrome mirror the abnormalities seen in schizophrenia. DSM–IV criteria specify the need for a ‘pervasive pattern of social deficits’, ‘cognitive or perceptual distortions’ and ‘eccentricities’ of behaviour (American Psychiatric Association, 1994). These abnormalities must not occur exclusively in the context of schizophrenia, affective disorder with psychotic features, other psychotic disorder or a pervasive developmental disorder.

The prevalence of schizotypy is higher in clinical than in non-clinical samples, and the prevalence within the families of people with schizophrenia is higher than the population prevalence, at about 10% (Kendler & Gardner, 1997).

Schizotypy includes some of the features of schizophrenia and schizoaffective disorder (Box 1) and is often apparent by early adulthood. However, schizotypal personality traits may be apparent in childhood or adolescence. A major factor distinguishing schizotypy from schizophrenia and other psychoses is the transient nature of psychotic experiences.

People with schizotypy often demonstrate poor social interactions. In addition to this and their attenuated psychosis-like experiences, they often show deficits in cognitive function, which are similar to those seen in schizophrenia but less severe. Schizotypy and schizophrenia tend to co-occur in families, suggesting that there may be shared susceptibility factors. However, schizotypy does not occur only as a precursor to schizophrenia. Rather, it appears to be an alternative expression of an underlying vulnerability which may or may not herald the onset of schizophrenia.

The schizophrenia spectrum
Diagnostic criteria for schizophrenia are necessarily somewhat arbitrary owing to limitations in our knowledge of the aetiopathology of the disorder. This leads to dilemmas regarding the definition of boundaries and the recognition that many of the clinical features of schizophrenia are dimensionally distributed.

It is recognised that schizophrenia and schizotypy share some genetic susceptibility factors. In addition, twin studies suggest that a predisposition to disease is transmitted but is not necessarily expressed as schizophrenia. Family studies indicate that a range of clinical conditions are more frequent in the relatives of people with schizophrenia (Lichtermann et al, 2000). These include schizoaffective disorder, atypical and schizophreniform psychoses, affective psychoses with mood-incongruent delusions as well as schizotypal personality disorder (Box 2Go). Thus it is possible that shared susceptibility factors may result in the expression of a variety of clinical phenotypes. These disorders can be considered as parts of the schizophrenia spectrum, a constellation of related but clinically diverse conditions.