Neuroanatomical Changes in Schizophrenia: Twin Studies

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Neuroanatomical Changes in SchizophreniaTwin
Studies

• Adam Bacchus
• 971227050
• PSY346F Presentation
• 20 Nov. 2003

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Introduction Why Twins?

• Studies with MZ twins discordant for
  schizophrenia
• Control for genetics, education, upbringing, etc.
• Reduce variability between patients and controls.
• -more power to distinguish effect
• Allow an idea of non-genetic aspects of disorder
  MZ prevalence (40).

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General Morphology

• Focused 3D MRI study schizophrenic brains
  smaller in all dimensions.
• Or maybe no difference in whole brain volume.
• -not main question of study not as thorough
• Or smaller volume of grey matter in left temporal
  lobe.

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Thalamus and Caudate

• Key structures of fronto-striato-thalamic
  pathways.
• Thalamus
• -key relay for sense and other info
• -takes input from hippocampus
• -some (non-twin) fMRI studies conflicted on
  level of function in schizophrenia
• -boundaries blurred by white matter hard to
  tell size in MRI size often reported small or
  unchanged
• -only twin MRI study says size is same for both
  twins

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Thalamus and Caudate (Contd)

• Basal Ganglia/Caudate
• -as well as movement, control regulation of
  affect
• -conflicted data on metabolism rates meds?
• -unmedicated studies (non-twin) suggest
  hypofunctioning
• -caudate usually seen larger in schizophrenia
  probably meds (supported by naïve studies and
  switching drugs)
• -twin MRI study larger caudate shows slight
  correlation with duration on antipsychotics

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Cerebral Cortex

• MZ twin MRI
• Lateral and 3rd ventricles enlarged in ill twin.
• Hippocampus smaller in ill twin.
• No correlation to meds or length of illness.
• Bilateral changes more obvious on left.
• Changes dont progress may be premorbid
• Is schizophrenia linked to early maldevelopment
  of cortex?

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Cerebral Cortex (Contd)

• Schizophrenia as maldevelopment?
• Need abnormality that implicates
  neurodevelopment.
• Cortical gyri formed mostly prenatal
• Abnormal gyri would show maldevelopment.
• But gyri no different in MZ twins.

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Cerebral Cortex (Contd)

• Brain damage hypotheses
• Left-handedness more prevalent in schizophrenia
  brain damage and abnormal laterality?
• Case study
• -fMRI sick twin uses both hemispheres for
  speech
• -H-MRS deficits bilaterally in hippocampus -
  ill twin
• -brain damage?
• -one hemisphere? Just hippocampus?

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Cerebral Cortex (Contd)

• Brain damage contd
• Smaller hippocampus, large ventricles in sick
  twin linked to perinatal complications.
• NOT pregnancy complications.
• Case study
• -low birth weight linked to poor premorbid
  functioning in sick twin
• -MRI high intensity signals in parietal white
  matter, large ventricles in sick twin similar
  to preemies
• -also traumatic birth (9hrs, vacuum extraction)

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Cerebral Cortex (Contd)

• Brain damage contd
• Interaction between low birth weight and
  perinatal trauma?
• Does low birth weight represent subgroup of poor
  premorbid functioning?

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Summary

• Link of schizophrenia to early damage.
• Ventricles and hippocampus (cortex).
• Trauma theory may explain stability.
• Why adult onset?
• Problem with twin studies sample size!
• Chicken or egg?
• So

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For the Future

• Ideal MZ twin study
• Large sample size.
• Follow infant pairs at risk repeated MRIs
• Stay with ones that become discordant.
• Try to establish primary/secondary nature of
  deficits.