Obsessive-Compulsive Disorder (OCD)
Causes and Risk Factors
While the causes of OCD are not fully understood, several genetic, neurobiological, and environmental factors appear to be at least partially involved.
Brain Structure and Function
Multiple neuroimaging and neurophysiology studies have identified abnormal activity in specific regions of the brain in patients with OCD; researchers are also investigating the possibility that structural abnormalities exist in specific parts of the brain in OCD patients. A report of a patient whose severe OCD disappeared after a small stroke destroyed a small, specific part of the brain supports the theory that disturbances in localized brain regions are involved in OCD (Nakao 2014; Pallanti 2011).
Additional support for the central role of the brain in OCD comes from a significant body of evidence that OCD is associated with abnormal activity of the neurotransmitters dopamine and serotonin (Koo 2010; Hesse 2005; Denys 2004). More recent evidence suggests that dysregulation of the excitatory neurotransmitter glutamate may also contribute to OCD (Kellner 2010; Pittenger 2011).
Variants of genes involved in serotonin, glutamate, and dopamine metabolism have been implicated in OCD (Pauls 2014; Delorme 2009; Nicolini 2010). More studies are needed to establish the specific role of particular genes in OCD, and to develop therapies on the basis of these discoveries (Stewart 2013; Mattheisen 2015).
In women and men, estrogen and progesterone levels, as well as individual differences in an estrogen receptor gene, have been associated with obsessive-compulsive symptoms (Alonso 2011; Hill 2007; Boon 2011; Avgoustinaki 2012). Estrogens are known to influence neurotransmitter pathways implicated in OCD, including serotonin, dopamine, and glutamate (Alonso 2011).
In one study, women on hormonal contraception consisting of both a progestin (a synthetic, progesterone-like compound) and estrogen exhibited less depression and OCD symptoms than those on progestin-only or no hormone therapy (Young 2007). In a rodent model, progesterone administration reduced OCD-like behavior (Umathe 2009). While there is evidence to suggest that sex hormones may be related to OCD symptoms, further studies are needed to clarify these relationships, and to establish whether manipulating hormone levels will be of therapeutic value for people with OCD.
Other Risk Factors
Stress. Studies have demonstrated that environmental and genetic factors contribute approximately equally to OCD risk. Life events such as stress or trauma may serve as “epigenetic modifiers” (meaning they modify gene expression and function without altering the sequence of specific genes) that impact serotonin, dopamine, and glutaminergic pathways (Pauls 2014; Mataix-Cols 2013; Cath 2008).
Gender. Men and women are equally affected by OCD, though the symptom subtype does differ between genders. Women are more likely than men to exhibit contamination obsessions and cleaning compulsions, and less likely to have sexual or religious obsessions (Labad 2008; Veale 2014; Landeros-Weisenberger 2010).
Age. The average age of OCD onset is early 20s in women and late adolescence in men (Veale 2014). Earlier age at onset is associated with greater incidence of the symmetry subtype, sexual or religious obsessions, and a greater likelihood of tic disorders (Janowitz 2009; Labad 2008).
Family history. OCD risk is markedly higher for first-degree relatives of patients with OCD or Tourette’s syndrome (Yip 2014).
Pregnancy. In a rigorous review of studies on OCD prevalence in women, pregnancy increased the risk of OCD 1.45-fold, and post-partum women were 2.38 times as likely to experience OCD (Russell 2013).
Infection. Rarely, OCD in children appears to be caused by a group A βhemolytic streptococcal infection that results in a rapid onset of symptoms. This is an autoimmune condition known as “pediatric autoimmune neuropsychiatric disorder associated with Streptococcus infection,” known by the acronym PANDAS. Encephalitis and bacterial or viral infections have also been associated with the onset of OCD (Ercan 2008; Murphy 2010; Yip 2014; Sudak 2012).
Central nervous system trauma or disease. OCD symptoms can sometimes be associated with other neurological conditions, such as stroke, brain tumor, trauma to the frontal lobe, Huntington’s disease, Tourette’s syndrome, frontotemporal dementia, or hypoxia (Pallanti 2011; Veale 2014; Yip 2014).