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Revision Notes SC326 Term 2
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Detailed notes on each lecture in term two of SC326, including detailed annotations on each key reading
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SC326 – PSYCHIATRY AND MENTAL ILLNESS (TERM 2)WEEK 16 – GENETICS AND MENTAL ILLNESS
Key info
- EUGENICS = The selection of desired heritable characteristics in order to
improve future generations, typically in reference to humans
- There is a dominance in psychiatry that mental illness is biological
- It is important to discuss all possibilities
Heredity and hereditability
- Before the 19th century, hereditary was not seen as biological
- Hereditary was understood as transmission within a family or from one
generation to the next
- From legal inheritance to the transmission of physical and personal traits, to
the transmission of disease
- Pathology belongs not just to the individual but to the family
Hereditary and hygiene
- Causes of insanity: psychological hereditary vs. moral sickness
- Psychiatry as public health – ‘moralization of the masses’ and ‘family hygiene’
- Rise of physiological hereditary alongside rise of hospital medicine and
medical statistics
- Heredity as explanation in absence of physical signs of pathology
George Mendel (1822-1884)
- Founder of modern genetics
- Breeding pea plants
Dominant and recessive traits
Mendelian inheritance – effects of single genes
Emil Kraepelin (1856-1926)
- ‘Hereditary degeneration’ as cause of psychosis
- Sought to identify early indicators for the process of degeneration
- Saw future of psychiatry as “the discovery of laws that govern the transmission
of diverse traits associated with insanity”
- Eugenicist and proponent of racial hygiene
Ernst Rudin (1874-1952)
- Kraepelin’s student
, - First large scale family study with siblings on dementia praecox (later
relabelled schizophrenia)
- Disproved his and Kraepelin’s hypothesis that schizophrenia resulted from a
single gene (Mendelian inheritance)
- Actively involved in the development of Nazi Eugenics
Nature/nurture
- To what extend is mental illness biologically based
- To what extent is it caused by other factors such as environment, parenting
and other ‘cultural determinants’
- Twin studies = same biology
- Adoptive studies = different biology
Twin studies
- Compare the degree of concordance between identical (monozygotic) and
non-identical (dizygotic) twins
- If heredity is important you would expect higher concordance in MZ than DZ
twins
- Since MZ are fertilised from a single egg and are genetically identical at
conception
- Research has largely focused on schizophrenia as a severe mental illness
where heredity has been thought to play a more important role
- Such studies are not easy to carry out as identical twins are not common
- Those where at least one has a diagnosis of mental illness is even less common
Kallman’s twin studies
- Early studies found far higher levels of concordance for schizophrenia in MZ
than DZ
- 85.8% in MZ and 14.7% in DZ
- This suggests that genetic factors played a key role in causation
- However, there were major methodological problems
- Kallman personally decided whether the twins were identical or not (no
precise tests at time)
- Kallman also made the diagnosis
- More recent data still shows a significant different in the level of concordance
with MZ and DZ
- However, not as large as Kallman found
The limitations of twin studies
- Concordance between MZ and DZ studies could result from environmental
factors
, - E.g., identical twins are often treated in much more similar ways than non-
identical twins
- This has led to the use of adoption studies as an alternative approach to
studying heredity
Adoption studies
- Focus on the children of mother’s diagnoses with schizophrenia adopted at
birth
- The occurrence of schizophrenia in these children is then compared with its
occurrence in adopted children, whose biological mothers do not have
schizophrenia
- Finding such cases is not easy since the mother must have schizophrenia and
had a child adopted (both relatively rare events)
- Adoption studies show that if a mother has had schizophrenia then the
offspring are more likely to also have schizophrenia
- Even if not reared (bought up) by her
- There is often some environmental matching in adoption that may influence
these results
- E.g., in terms of social class and cultural influences
Genomics
- Human genome project (1990-2003)
- US initiative to sequence and map the human genome
- Was believed that understanding the genome would lead to radical change in
how we understand and treat illness
- Creation of the human genome made it easy to study diseases associated with
mutations in a single gene (mendelian disorders)
- But not so simple with complex diseases like cancer, cardiovascular disease
etc.
- Mental disorders do not depend on the presence or absence of single genes,
but many
Genome-wide association (GWA) studies
- Researchers compare the genotypes of thousands to hundreds of thousands
of individuals with and without a specific disease or condition
- GWA studies are not easy to carry out
- Large samples are required and therefore huge amounts of data that are
difficult to manage and interpret
Epigenesis and epigenetics
, - Genomics has largely abandoned notion that single genes play a causal role in
the development and onset of mental illness
- GWA studies show that the genetic contribution comes from the combined
effects of many genes
- Not just a few
- Increasing acknowledgement of the role of environment in affecting the
expression of genes
- A process known as epigenesis, who’s study is termed epigenetics
- More away from the idea that genes provide a ‘blueprint’ of human behaviour
- Looking at genes alone is not helpful because they are ‘turned on and off’ by
environmental factors
Social and ethical implication of genetic markers of mental illness
- Promises to improve classification and therefore diagnosis of mental illnesses
- Promise of biological markers linked to early prediction i.e., assessing children
before symptoms appear
- Early intervention/treatment
Ethics of prediction
- Biomarkers are not the cause of disorders
- they are an estimation of the probability of whether a condition is present or
will develop
- e.g., combining data on genetic predisposition with social and environmental
risk factors like family poverty or child abuse
- limits of existing methods of finding genetic causes of mental illness (twin
studies, adoption, genomics) doubts about whether predictive value is strong
enough
- ethical questions of whether we should predict people’s likelihood of
developing a mental illness
- also, whether we should intervene at early stages of development
- children and adolescents ‘at risk’ – pre-symptomatic treatment?
- Prevalence and social groups (race, class, gender) – further marginalisation
and discrimination
- Data ownership and privacy – who owns data and how will they use it
Genetics, mental illness, and eugenics
- Eugenics has not happened in the UK
- It suggests preventing a certain illness from progressing by stopping certain
people from breeding (reproducing)
- Difficult to determine what is seen a as a “good characteristic” this can vary
between cultures, societies, and countries
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