Research evidence suggests quite a high inheritance factor for OCD,certainly when compared to other disorders.
CAREY AND GOTTESMAN found an 87 percent concordance rate in identical twins for OCD, whereas MCGUFFIN found a concordance rate for schizophrenia for identical twins was only 46 percent.
However, these concordance rates are not 100 percent, which means that environmental factors must play a role too.
OCD and other disorders- PAUL AND LECKMAN studied patients with tourettes syndrome, and their families and concluded that OCD is one form of expression of the same gene that determines tourettes. Obsessive behaviour is also typical of anorexia, and is one of the characteristics distinguishing individuals with anorexia from individuals with bulimia.
The COMT gene A study by SCHINDLER confirmed the association between OCD and the COMT gene. Other candidate genes have also been discovered that link with OCD.
WENDLAND identified a gene involved in serotonin production in OCD patients. WELCH found that mice lacking this gene compulsively groomed themselves to the point of self injury and shower greater anxiety than normal mice.
Biochemical explanations are supported by research studies of the effects of drugs. KIM found that drugs raised levels of serotonin also reduced dopamine levels in the right basal ganglia. Reduction in dopamine levels was positively correlated with reduction of obsessive compulsive symptoms assessed using Y-BOCS.
Neuroanatomical explanations are also supported by research evidence. For example PET scans indicate that OCD patients exhibit increased glucose metabolism in the OFC- caudate nuclei loop. When compared with control subjects, people with OCD burn more energy rapidly in this network. This increased metabolism is also correlated with the severity of OCD.
However in a recent study MORITZ ET AL has questioned the role of the OFC, because OCD patients did not perform abnormally on cognitive tasks relating to the OFC. The researchers concluude that OFC dysfunction may be more subtle than previously claimed.