explaining OCD

• what is the genetic explanation?

  • the mental disorder is inherited
  • we can look at the explanation through twin studies and family studies
• twin study?

  carey and gottesman ( 1981 )

  found that identical twins showed a concordance rate of 87 % for obsessive symptoms

  compared to 47% in non identical twins

  suggests that genetic factors are moderately important
• twin study?


  van grootheest et al ( 2005 )

  found that the concordance rate for identical twins was higher than non identical twins

  concluded that the concordance rates for identical twins were

  not exactly 100 %, showing that environmental

  factors also play a role
• family studies?

  nestadt et al ( 2000 )

  identified 80 patients with ocd and 343 of their first degree relatives and compared them to 73 control patients sithout mental illnes and 300 of their relatives

  they found that lifetime incidence of ocd was higher in relatives of ocd patients ( 11.7 % ) compared to relatives of healthy controls ( 2.7 % )
• family studies?

  Frontenelle et al ( 2004 ) compared patients with OCD in Brazil, North America, Latin America, Europe, Africa and Asia.

  
  

  Most patients in all cultures had a mixture of obsessions and compulsions.

  
  

  It was concluded that core features of OCD are probably independent of cultural variations.
• evaluation?

  both genetic factors and environmental factors are important

  concordance rates in identical twins may be higher due to environmental reasons in which identical twins are brought up in more similar environments than non identical twins
• evaluation?

  Environmental factors also play a role in explaining why the incidence of OCD is higher among the relatives of patients than among the relatives of healthy controls.

  Close contact with a relative suffering from OCD may be very stressful and the stress created may increase the chances of developing the disorder.
• evaluation?

  if only genetic factors are important , the concordance rate should be 100 %

  the actual figure is consistently lower than 100 % indicating that environmental factors are important
• the COMT gene?

  tukel et al , 2013

  • the COMT gene is involved in the production of catechol -O- methyltransferase
  • this regualtes the production of the neurotransmitter dopamine
  • one form of the COMT gene has been found to be more common in OCD patients
  • this variation produces lower activity of the COMT gene and high levels of dopamine
• the SERT gene?

  • the SERT gene affects the transport of the serotonin creating lower levels of this neurotransmitter
  • these lower levels are also implicated in ocd
  • one study found a mutation of this gene in 2 unrelated families where 6 of the 7 family members had ocd ( ozaki et al 2003 )