Transcript Gottesman & Shields 1966

 To
see whether schizophrenia had a genetic
basis
 Used a twin study methodology to investigate
the concordance rates of schizophrenia in
twins
 They replicated previous studies to test
reliability
 Researchers
looked at patient records from a
psychiatric hospital. From 1948 – 1964.
 392 patients were twins of the same sex, and
of those, 68 had a diagnosis of schizophrenia.
 Although 6 patients were discounted either
because their twin was unable to participate
or it was unclear if they were MZ or DZ
twins.
 This left 62 patients, 5 twin pairs were
already on the register. 52 patients twin
were tracked down to participate.
 Out
of the 62 patients, half were male and
half were female.
 Ages ranged from 19 – 64, with an average
age of 32.
 It was determined whether they were MZ or
DZ twins by using three methods. Fingerprint
testing, blood testing, and resemblance
testing (DNA testing was not around at this
time)
 Data
used for this study came from.
 Hospital notes, case histories based on self
report questionnaires and interviews with
twins and parents, tape recorded 30 minute
samples of verbal behaviour and semi
structured interviews, personality testing,
testing to measure disordered thinking
(conducted on both twins and parents)
 If
one twin had been diagnosed researchers
wanted to know if the other twin would soon
be diagnosed. (using concordance rates)
 The data was analysed between the twin who
was first admitted and their other twin. With
twins being categorised in 4 ways.
 Category
1 – Both twins had been diagnosed
with schizophrenia
 Category 2 – First twin has schizophrenia, but
the other twin had another diagnosis related
to schizophrenia
 Category 3 – The 2nd twin had some
psychiatric abnormality that wasn’t related
to schizophrenia
 Category 4 – The first twin had schizophrenia
but the 2nd twin was analysed as normal
 10
MZ twins
 3 DZ twins
3
MZ twins
 6 DZ twins
6
MZ twins
 9 DZ twins
5
MZ twins
 18 DZ twins
 Severe
schizophrenia (longer than 2 years)
 MZ – 75%
 DZ – 22%
 Mild
schizophrenia (less than 2 years)
 MZ – 17%
 DZ – 0%
 There
was a significant difference found
between MZ and DZ twins in all measures.
 MZ twins were always more similar in
diagnosis than DZ twins. In each case where
the co-twin had some diagnosis.
 Concordance rates were higher in MZ and DZ
twins for severe schizophrenia compared to
mild schizophrenia.
The findings suggest the closer the genetic
relationship between two people, the greater
the chance that both people in that relationship
will be diagnosed with schizophrenia or a related
psychotic disorder.
 However, as in MZ twins the concordance rate
was not 100% it cannot be solely down to genes.
However it does show that genetic factors to
predispose someone to schizophrenia alongside
environmental triggers.
 11 other studies Gottesmen and Shields looked
at showed results did support each other.

 It
would have been useful to know more
about what ‘related psychosis’ meant when
describing the schizophrenia scale to take
into account the related disorders as they
fail to make this clear.
 Gottesman and Shields suggested that there
are different types of schizophrenia and
some might be caused by life events
(environmental stimuli) such as being a
prisoner of war, and it was to distinguish
between the types and results of the study.