230 - candidate genes found more frequently in people with OCD e.g SERT gene - affects reuptake in the serotonin system
OCD is polygenetic
Evidence for heritability of OCD coming from family
in general population likelihood of OCD is 2% - however, the more closely genetically you are related to someone means higher concordance
first degree relative - 10%
Dz twin - 31%
Mz twin - 68%
Neural explanation - biochemical causes and an imbalance of neurotransmitters
Low levels of serotonin
are thought to cause obsessive thoughts - low levels of serotonin are thought to be removed too quickly from synapse before it can transmit a signal
presynaptic neurons
release neurotransmitters and receptors in the postsynaptic neuron detect these - if signal is strong enough
then message is passed on and taken back up to the presynaptic neuron by reuptake
if the process happens too quickly people with OCD will have a reduced serotonin level in the synapse - the SERT gene is responsible got serotonin transportation in the synapse
Neural structure - worry circuit
Obitofrontal cortex (OFC) - rationalises decision making
basal ganglia system - caudate nucleus and the thalamus
communications in the worry circuit appears to be overactive in people with OCD
in normal circuit basal ganglia filters out minor worries from the OFC - if overactive small worries get to thalamus, being passed back to OFC forming a loop
repetitive motor functions
attempt to break this loop - may give temporary relief but worry circuit will soon resume
issues in family and twin studies
twins have similar environments - Mz twins will be treated more similarly than Dz twins . - concordance rate for Mz is 68% although they share 100% of genetics suggesting OCD cannot be completely determined by biological factors and there are some enviromental
Diathesis stress response may be a more valid explanation
OCD is inherited genetic through genetic vulnerability - disorder does not develop unless there is an environmental stressor
research - 54% of 265 participants with ocd have one traumatic life events - those with trauma saw more severity of OCD symptoms
neuroimaging - using PET scans
Pet scanners - show hyperactivity of the OFC in people with OCD while scanning brain at rest and when symptoms stimulates - however, this is a correlation study - researchers cannot be sure if this is a consequence of ocd or if the is a cause of ocd