Causes of Schizophrenia

483
Schizophrenia
Causes of Schizophrenia
The search for causes of schizophrenia has been more intense than for any other psychological disorder. The findings so far confirm one thing for certain: As with other
disorders, biological, psychological, and sociocultural factors combine to cause or
worsen all forms of schizophrenia (Sullivan, Kendler, & Neale, 2003).
Biological Factors Research in behavioral genetics shows that schizophrenia runs
CATATONIC STUPOR The symptoms
of schizophrenia often occur in characteristic patterns. This woman’s lack of motivation and other negative symptoms of
schizophrenia are severe enough that she
appears to be in a catatonic stupor. Such
patients may become rigid or, as in this
case, show a waxy flexibility that allows
them to be “posed” in virtually any position. Diagnosticians using the traditional
subtype system would probably label her
as displaying catatonic schizophrenia.
in families (Asarnow et al., 2001; Gottesman, 1991). One family study found that 16
percent of the children of mothers with schizophrenia—compared with 2 percent of
those of mothers without schizophrenia—developed schizophrenia themselves over a
twenty-five-year period (Parnas et al., 1993). Even if they are adopted by families without schizophrenia, the children of parents with schizophrenia are ten times more likely
to develop schizophrenia than adopted children whose biological parents do not have
schizophrenia (Kety et al., 1994). Still, it is unlikely that a single gene transmits schizophrenia (Chumakov et al., 2002; Plomin & McGuffin, 2003). Among identical-twin
pairs in which one of the members displays schizophrenia, 40 percent of the other
members display it, too; but 60 percent of them do not (McGue, 1992). It is more likely
that some people inherit a predisposition, or diathesis, for schizophrenia that involves
many genes (e.g., Harrison & Law, 2006; Ma et al., 2006; Mah et al., 2006; Peirce et al.,
2006). This diathesis then combines with other genetic and nongenetic factors to cause
the disorder (Moldin & Gottesman, 1997).
The search for biological factors in schizophrenia also focuses on a number of
abnormalities in the structure, functioning, and chemistry of the brain that tend to
appear in people with schizophrenia (e.g., Andrews et al., 2006; Neves-Pereira et al.,
2005; Tamminga & Holcomb, 2005). For example, brain imaging studies have compared patients with schizophrenia with other mental patients. Many patients with
schizophrenia (especially those who display mostly negative symptoms) have less tissue in areas of the brain that are involved in emotional expression, thinking, and information processing—functions that are disordered in schizophrenia (Conklin & Iacono,
2002; Csernansky et al., 2004; Gilbert et al., 2001; Highley et al., 2003; Pol et al., 2002;
Selemon et al., 2003; Sigmundsson et al., 2001; Velakoulis et al., 2006). There is also
evidence that worsening symptoms are associated with continued tissue loss in these
areas (Ho et al., 2003). Patients with mainly positive symptoms tend to have essentially normal-looking brains (Andreasen, 1997).
Researchers are also investigating the possibility that abnormalities in brain chemistry—
especially in neurotransmitter systems that use dopamine—play a role in causing or
intensifying the symptoms of schizophrenia (Seeman et al., 2005). Because drugs that
block the brain’s dopamine receptors often reduce the hallucinations, disordered thinking, and other positive symptoms of schizophrenia, some investigators speculate that
schizophrenia results from excess dopamine. However, the relationship between
dopamine and schizophrenia is a complex one (Albert et al., 2002; Koh et al., 2002).
Some research suggests, for example, that excessive activity in dopamine systems may
be related to the appearance of hallucinations, delusions, and other positive symptoms
of schizophrenia. Abnormally low dopamine system activity, especially in prefrontal
brain areas, has been associated with negative symptoms such as withdrawal (e.g.,
Cohen & Servan-Schreiber, 1992).
Some researchers are integrating genetic and environmental explanations of schizophrenia by looking for neurodevelopmental abnormalities (e.g., Rapoport, Addington,
& Frangou, 2005). Perhaps, they say, some forms of schizophrenia arise from disruptions in brain development during the period from before birth through childhood,
when the brain is growing and its various functions are maturing. For instance, prenatal exposure to physical trauma, flu, or other infections is associated with increased
risk for developing schizophrenia (AbdelMalik et al., 2003; Brown et al., 2004, 2005;
Malaspina et al., 2001). It may be that the expression of a genetically transmitted predisposition for brain abnormality is enhanced by environmental stressors such as maternal drug use during pregnancy, complications during birth, and childhood malnutrition
484
in review
Chapter 12 Psychological Disorders
SCHIZOPHRENIA
Aspect
Key Features
Common
Symptoms
Disorders of
thought
Disorders of
perception
Disorders of emotion
Disturbed content, including delusions; disorganization,
including loose associations, neologisms, and word salad
Hallucinations or false perceptions; poorly focused
attention
Flat affect; inappropriate tears, laughter, or anger
Possible Causes
Biological
Psychological and
sociocultural
?
Genetics; abnormalities in brain structure; abnormalities in
dopamine systems; neurodevelopmental problems
Learned maladaptive behavior; disturbed patterns of family
communication
1. The
approach forms the basis of the vulnerability theory of
schizophrenia.
2. Hallucinations are
symptoms of schizophrenia; lack of emotion is a
symptom.
3. Patients with schizophrenia who were able to finish school are
likely to
show improvement.
(Sørenson et al., 2003). Neurodevelopmental factors may help explain why children of
parents with schizophrenia tend to show cognitive and intellectual problems associated
with brain abnormalities (Ashe, Berry, & Boulton; 2001; Cannon et al., 1994;
McGlashan & Hoffman, 2000; Neumann et al., 1995).
Psychological and Sociocultural Factors Psychological factors alone are not
considered to be primary causes of schizophrenia (Bassett et al., 2001), but psychological processes and sociocultural influences can contribute to the appearance of schizophrenia and influence its course. These influences include poverty and other adverse
living situations, maladaptive learning experiences, dysfunctional cognitive habits, and
stressful family communication patterns (Cantor-Graae & Selten, 2005; Wicks et al.,
2005). For example, individuals with schizophrenia who live with relatives who are critical, unsupportive, or emotionally overinvolved are especially likely to relapse following improvement (Hooley, 2004; Rosenfarb et al., 2000; Wearden et al., 2000). Family
members’ negative attitudes may be a source of stress that actually increases the chances
that disruptive or odd behaviors will persist or worsen (Rosenfarb et al., 1995). Patients
who are helped to cope with these potentially damaging influences tend to have better
long-term outcomes (Bustillo et al., 2001; Velligan et al., 2000).
Vulnerability Theory All the causal theories of schizophrenia we have outlined are
consistent with the diathesis-stress approach, which assumes that stress activates a person’s predisposition for disorder. (“In Review: Schizophrenia” summarizes these theories,
as well as the symptoms of schizophrenia.) In fact, a diathesis-stress framework forms the
basis for the vulnerability theory of schizophrenia (Cornblatt & Erlenmeyer-Kimling, 1985;
Zubin & Spring, 1977). This theory suggests that (1) vulnerability to schizophrenia is
mainly biological; (2) different people have differing degrees of vulnerability; (3) vulnerability is influenced partly by genetic influences on development and partly by abnormalities that arise from environmental risk factors; and (4) psychological components,
such as exposure to poor parenting, a high-stress environment, or inadequate coping