Schizophrenia – a Genetic and Environmental Review

Introduction

Schizophrenia is defined as "a severe brain disorder characterized by disturbances of thoughts, perceptions, volition, and cognition, which affects about 1% of the world population today" (Ozawa et al., 2006, p. 546). The disorder can be incapacitating to those who live with it, preventing normal societal function. Despite its frequency in the population, scientists and medical professionals still struggle to find a conclusive explanation for why some people develop schizophrenia.

This may be, in part, due to its ties to both environmental and genetic factors.

Throughout the literature, there are extensive hypotheses on what the contributing factors to the development of the disorder are, but a consensus remains that no one factor defines susceptibility. Environmentally, the adult onset of schizophrenia seems to be linked to neonatal care. Maternal viral infection (Ozawa et al., 2006), as well as maternal vitamin D deficiency from improper diet and sunlight intake (Pluta, 2010), leads to small but significant increases in offspring disorder development.

Genetic predisposition is also a well-known factor to be considered. Currently well researched, disruption of dopaminergic pathways in schizophrenic patients is becoming more prevalent as it seems to play a crucial role in the symptomology of the disorder. More specifically, abnormal dopamine function appears to give rise to much of the positive symptoms (psychosis) (Abi-Dargham et al., 2000).

In addition to the factors that increase the likelihood of development, treatment is heavily discussed in the literature. Medication is a crucial baseline component of treatment as it can keep patients functional, so that other psychosocial therapies can occur. Unfortunately, the symptomology that demands medication also prevents approximately 50% of patients from maintaining a regimen. Increased numbers of environmental treatments are being researched to rectify this (Velligan et al., 2008).

Schizophrenia is generally a hard disease to measure because its symptoms vary widely across the population. The two domains that most of the symptoms fit within are positive and negative. Positive symptoms are analyzed using the Brief Psychiatric Rating Scale. This scale accurately places how severe a patient's symptoms (psychosis, delusions, etc.) are and detects changes over time.

The Scale for the Assessment of Negative Symptoms (SANS) rates how severely a patient presents in the five categories on the scale (Lindenmayer, Harvey, Khan, & Kirkpatrick, 2007). Unfortunate limitations to these measurement scales are that patients frequently go on and off medications, making it hard to monitor improvement in symptoms over time. Also, patients can cross lines from one subtype to another, as well as more minor subtypes, making categorization difficult.

Literature Review Genetic Studies

Common characteristics in schizophrenic patients include anxiety, impaired motor coordination, and working memory dysfunction; however, in our study, these characteristics were not affected (Hikida et al., 2007). When we inserted a shortened DISC1 transgene into C57BL/6 mice, we observed significant pathogenic and behavioral traits consistent with schizophrenia in the resulting transgenic (tg) mice lines.

Our findings contribute significantly to the existing literature claiming that the DISC1 is implicated in some aspects of schizophrenic symptomology and development. Since the transgene was derived from a human source, this study holds substantial external validity for generalizing the results to the human population. However, we must always be aware of potential limitations, such as changes in the pathology and behavior of the disease after years of medical treatment or psychological therapy (Hikida et al., 2007).

Schizophrenia is hypothesized to be the result of both genetic and environmental factors. A prominent environmental factor that might contribute to the fetal development of schizophrenia is maternal contraction of a viral infection. Previous studies presented compelling evidence suggesting that maternal viral infection during pregnancy could lead to higher rates of fetal schizophrenic development.

Research indicates that the type of viral infection—whether influenza, polio, rubella, or measles—is nonspecific and might all yield the same outcomes. This discovery led researchers to theorize that perhaps the maternal cytokine immune response, rather than the viral infection itself, might be responsible for disrupting fetal neurological development. To model this environmental factor of schizophrenic development, we employed double-stranded RNA polyriboinosinic-polyribocytidilic acid (poly I:C).

We used this methodology to mimic a viral infection because it spurs a nonspecific immune reaction. BALB/c mice were bred in the lab, and pregnant females were injected daily with the double-stranded RNA from two to three weeks post-fertilization (Ozawa et al., 2006). We then assessed if the offspring of the poly I:C-injected mothers exhibited characteristics of schizophrenia by measuring maturational delay, dopaminergic system damage, and cognitive impairment.

In addition to cognitive impairment, we also studied the effects of two common anti-psychotic drugs, clozapine and haloperidol, on these symptoms. We found significant dopaminergic system damage and cognitive impairment in the adult offspring of these mice. Both clozapine and haloperidol proved to ameliorate the symptoms of cognitive impairment (Ozawa et al., 2006).

Although our study provides a valuable animal model for understanding the connection between gestational viral infection and offspring schizophrenia risk, there are certain limitations when compared to a human model. Most significantly, we have yet ascertain at which stages of pregnancy an infection poses the greatest risk to the fetus. This factor can pose challenges for data collection in human studies, as women may not easily recall or report an early pregnancy viral infection, especially if they had been unaware of their condition.

Interestingly, while the immune system is more susceptible to contracting viruses in colder months like winter and spring, this is also the time of year that vitamin D deficiencies are most common. This period also coincides with significantly more babies born who will develop Schizophrenia in adulthood. The most direct way to gain vitamin D is through the skin being exposed to sunlight, which obviously becomes less feasible in the winter. Through the processing of vitamin D in the human body, 25-hydroxyvitamin D3 (25[OH]D3) is produced.

Infant blood samples from the Newborn Screening Biobank were analyzed for concentrations of 25[OH]D3. For this purpose, 424 Danish, schizophrenia, and control matched pairs were used (Pluta, 2010). The data showed a significant variation in the amount of 25[OH]D3 present in newborn blood throughout different months of the year. There was also a significant association between developing Schizophrenia in adulthood and the amount of 25[OH]D3 present in the blood at the time of birth.

In comparison to the fourth quintile of infants, infants with the highest 20% (first quintile) of 25[OH]D3 at the time of birth had a 1.71% relative risk of developing Schizophrenia in adulthood. However, those in the lowest 20% (fifth quintile) of 25[OH]D3 at the time of birth had a relative risk of 2.1% in comparison to the fourth quintile. The relative risks of developing schizophrenia in controls are shown below (Figure 3). The most interesting component of the research is that prenatal vitamin D plays a significant role in the future development of schizophrenia. However, the trend is neither linear nor simple. Both the first and fifth quintiles had a higher risk of disease development compared to the fourth quintile. It appeared, though, that vitamin D deficiency played a more prominent role (Pluta, 2010).

A literature analysis reveals that both genetic and environmental factors play a significant role in the development of schizophrenia. Multiple drug treatments for this disease are available, each with its own group of champions (Leucht, 2009). The effect of the environment on drug treatment and patient care for schizophrenia in general should also be considered.

Schizophrenia is a disease that often necessitates drug treatment to help patients function normally. However, adherence to medication is a significant problem in the population. The very symptomology that necessitates drug adherence can also promote patient dissociation from treatment. Three different environmental treatment approaches were used on subjects diagnosed with schizophrenia: full Cognitive Adaptation Training (CAT), Pharm-CAT, and Treatment-as-Usual (TAU). Full CAT is a personalized treatment designed to promote medication adherence through specific environmental set-up and organization in the home.

Pharm-CAT is essentially the same, but the organization pertains only to specifically medication-related lifestyle components (Velligan et al., 2008). The initial regimens lasted for a period of nine months, and medication adherence was measured by counting untaken pills during periodic home visits. After this period, the CAT environments were not removed; however, home visits were stopped for another six months.

Adherence to medication treatments was shown to be significantly higher in both Full-CAT and Pharm-CAT patients compared to usual treatment patients during all stages of the experiment. However, in the area of functional outcomes, Full-CAT patients only performed better than Pharm-CAT in the initial nine months of the study, and only Full-CAT patients outperformed traditional patients once home visits were removed (Velligan et al., 2008).

This study provides significant data to support how beneficial individualized environments can be in maintaining the normal function and medication compliance of schizophrenic patients. In all cases, patients with any form of CAT treatment outperformed those undergoing their usual treatment. However, the efficacy of this treatment seemed to decrease when regular check-ins on the patients ceased. This is an important distinction, as a limitation to this treatment is that it does not appear to be significantly effective in promoting self-sufficiency in schizophrenic patients (Velligan et al., 2008).

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