Schizophrenia and intellectual disability (mental retardation) can have organic or biochemical etiologies. Schizophrenia is characterized by distortions in thinking, perception, and behavior, and is associated with abnormalities in brain structure and function as well as imbalances in neurotransmitters like dopamine. Genetic factors, complications during birth or pregnancy, and infections may contribute to changes in brain chemistry and structure. Intellectual disability is characterized by below average intelligence and lack of adaptive skills, and around 25% of cases are linked to genetic abnormalities like Down syndrome, infectious diseases during pregnancy, or environmental toxins that can damage the developing brain like mercury or lead.

1. Topic: Briefly describe psychiatric disorders with organic/biochemical etiology:
1. Schizophrenia.
2. Mental retardation (intellectual disability).
Psychiatric disorder:
Psychiatric disorder is a mental illness diagnosed by a mental health professional that greatly
disturbs your thinking, moods or behavior and seriously increases the risk of disability, death or
loss of freedom.
For example: Depression, Schizophrenia, Personality disorders, Anxiety disorders, and Eating
disorders etc.
Schizophrenia:
The word Schizophrenia derived from Greek word “Schizo” meaning splitting and “Phrenia”
meaning mind.
Schizophrenia is the chronic, severe mental disorder that affects the way a person thinks, express
emotions, perceives reality and relates to others.
According to WHO:
1. Schizophrenia is a chronic and severe mental disorder affecting 20 million people
worldwide.
2. Schizophrenia is characterized by distortions in thinking, perception, emotions, language,
sense of self and behavior.
3. Common experiences include hallucinations and delusions.

2. 4. Worldwide, schizophrenia is associated with considerable disability and may affect
educational and occupational performance.
Organic / biochemical etiology:
The exact cause of schizophrenia isn’t known but like cancer and diabetes, schizophrenia is a
real illness with a biological basis. Researchers have uncovered a number of things that appear to
make someone more likely to get schizophrenia including:
1. Genetics.
2. Brain chemistry and circuits.
3. Brain abnormality.
4. Environment.
Biochemical factors:
Certain biochemical substances in the brain are believed to be involved in schizophrenia,
especially a neurotransmitter called Dopamine. One likely cause of this chemical imbalance is
the person’s genetic predispositions to the illness. Complications in pregnancy or birth cause
structural damage to brain may also be involved.
The Role of Neurotransmitters:
Neurotransmitters play a role in schizophrenia. For years, dopamine was the focus of study, but
later findings led investigators to conclude that this one could not fully account for
schizophrenia. Other neurotransmitters are also the focus of study, such as serotonin, GABA and
glutamate.
Brain Structure and Function:

3. Abnormalities in schizophrenia involves enlargement of ventricles, dysfunction in the temporal
lobe, dysfunction in prefrontal cortex and surrounding brain regions.
Enlarged Ventricles:
Postmortem studies of the brains of people with schizophrenia consistently revealed enlarged
ventricles. The brain has four ventricles, which are spaces in the brain filled with fluid. Having
larger fluid filled spaces implies a loss of brain cells, Meta-analysis of several neuroimaging
studies have most consistently revealed that some people with schizophrenia, even very early in
the course of illness and across the course of illness, have enlarged ventricles.
Factors involving the Prefrontal Cortex:
A variety of evidence suggests that the prefrontal cortex is of particular importance in
schizophrenia.
 The prefrontal cortex is known to play role in behaviors such as speech, emotion, goal
directed behaviors, which are disrupted in schizophrenia.
 MRI studies have shown reductions in gray matter in the prefrontal cortex.
 People with schizophrenia perform more poorly on neuropsychological tests designed o
tap functions promoted by the prefrontal region, including working memory or ability to
hold bits of information in memory.
Problems in the Temporal Cortex and Surrounding Regions:
Additional research has found that people with schizophrenia have structural and functional
abnormalities in temporal cortex, including areas such as temporal gyrus, hippocampus,
amygdala and anterior cingulate. Other evidence indicates that the hypothalamic-pituitary

4. adrenal (HPA) axis is disrupted in schizophrenia. Taken together stress reactivity and a disrupted
HPA axis likely contribute to the reductions in hippocampal volume observed in people with
schizophrenia.
Mental Retardation (Intellectual disability):
Mental retardation is characterized by below average intelligence or mental ability and a lack of
skills necessary for day to day living.
People with mental retardation can and do learn new skills but they learn them more slowly.
There are varying degrees of mental retardation from mild to profound.
Someone with mental retardation has limitations in two areas. These areas are:
 Intellectual functioning ___ also known as IQ, this refers to a person’s ability to learn ,
reason, make decisions and solve problems.
 Adaptive behaviors ___ these are the skills necessary for day to day life such as being
able to communicate affectively, interact with others and take care of oneself.
A person with mental retardation have IQ less than 70 to 75.
Organic/Biochemical Etiology of Mental Retardation:
Causes of the mental retardation identified in 25 percent people are neurobiological.
Genetic or chromosomal abnormalities:
One chromosomal abnormality that has been linked with mental retardation is trisomy 21, which
refers to having an extra copy of chromosome 21. This is also known as Down syndrome. People
with down syndrome are mentally retarded as well as some distinctive physical signs such as
short and stocky stature; oval upward-slanting eyes etc.

5. Another abnormality is Fragile X Syndrome that can cause mental retardation and involve a
mutation in fMRI gene on the x chromosome.
Several hundred recessive gene diseases have been identified, and many of them involve in
mental retardation such as Phenylketonuria (PKU).
Infectious Diseases:
While in utero the fetus is at increased risk of mental retardation resulting from maternal
infectious diseases such as rubella. The consequences of these diseases are most serious during
the first trimester of pregnancy, when the fetus has no detachable immunological response that is
its immune system is not developed enough to ward off infection. Herpes simplex, HIV, and
syphilis are all maternal infections that can cause both physical and mental retardation.
Infectious diseases can also affect a child’s developing brain after birth.
Environmental Hazards:
Several environmental pollutants are implicated in mental retardation. One such pollutant is
mercury which may be ingested by eating affected fish. Another is lead, which is found in lead
based paints, smog, and the exhaust from automobile that burn leaded gasoline. Lead poisoning
can cause kidney and brain damage as well as anemia, mental retardation, seizures, and death.
References:
1. Laursen TM, Nordentoft M, Mortensen PB. Excess early mortality in schizophrenia.
Annual review of clinical psychology, 2014; 10, 425-438.
2. WebMD Medical reference by Smith Bhandari, MD on Jan 21, 2020.

6. 3. American Psychological Association.(2003). Diagnostic and statistical manual of mental
disorders.
4. Davison, G.C& Neale, J.M.(2001). Abnormal psychology, 8th edition. UK: John Wiley
and Sons.