Genetics affects gender differences in OCD

By: Ann Wang

Posted: 5/1/08

Like many psychiatric disorders, obsessive-compulsive disorder, or OCD, has an underlying genetic cause for many patients. Now a research team led by Ying Wang of the Hopkins School of Medicine has linked several genetic mutations to OCD and discovered that these mutations differ between men and women.

The study involved 219 families in which at least two siblings, or first or second degree relatives, like cousins, both had OCD. In each case, the symptoms of the disorder had developed before age 18.

Because the exact genes that cause the disease are not known, the research team looked for patterns shared by the chromosomes of those family members who had similar diagnoses.

These genes, which are located close together on a single chromosome and are often inherited together, are said to be linked. A linked genomic area common to many people with OCD suggests that the region may harbor genes that contribute to the disorder.

The research team found six mutations, all of them involving only one DNA base pair change, that were significantly associated with OCD. Four of these mutations were associated only with families where the affected members were all male.

None of these mutations were associated with families in which the affected members were all female. These results suggest a significant difference in what causes OCD to develop in men versus women.

Obsessive-compulsive disorder is classified as an anxiety disorder. A person with OCD suffers from repeated and obsessive thoughts and fears, such as of contamination by bacteria, of harming self or others, of moral doubts and so on.

People with OCD are known to have recurrent images of harming a loved one or of somehow contracting HIV. Compulsions are actions such as hand-washing, counting or getting HIV tests, that are performed to relieve the anxiety the obsessions cause.

People with OCD then feel anxious that the action was not enough to prevent the obsession from happening and must compulsively repeat the action.

OCD occurs with equal frequency in men and women, affecting one to three percent of the population. On average the symptoms of OCD develop at age 10, and usually before age 40, although people can go for many years without a clear diagnosis. Like autism and schizophrenia, the symptoms of OCD are expressed differently between genders.

Women with OCD are more likely to have contamination obsessions - anxiety about coming into contact with bacteria and contracting disease - while men are more likely to have aggressive or sexual obsessions. While the frequency of compulsions is equal between genders, women's compulsions have been shown to be more severe.

Symptoms are also more likely to develop in women during middle age, especially after pregnancy and delivery. Men develop tics such as Tourette's Syndrome, a related condition, at an earlier age and more frequently.

The results of this study are not comprehensive enough to explain all the differences in how OCD is expressed between genders, but they definitely suggest that the differences are genetically rooted.

The researchers speculate that sex hormones play a role in regulating the genes in question, or that in males, the Y-chromosome interacts with the cell's mitochondria to produce these differences.

The team plans to look at other variables in families that include people living with OCD. For example, the six mutations linked to OCD that they found were all located in a cluster of genes known to help process our sense of smell, suggesting that those with the disorder have changes in how they perceive smells. The team plans to pursue this link in future studies.