Numerous studies have established that OCD runs in families. If any of his first-tier relatives (parents, siblings) have OCD, your child's risk of developing the disorder increases 12 percent, more than four times the risk in the U.S. population as a whole. And there is evidence that this percentage may be even higher.

A 1990 study of relatives of children with OCD by Marge Lenane at the National Institute of Mental Health (NIMH) showed that 17 percent of parents and 5 percent of siblings met diagnostic criteria for the disorder. The authors of this study speculate that by loosening criteria to a wider spectrum of symptom severity, a full 30 percent of the children would have a close family member who also manifests the illness.

Michele, a mother of four, described her day-to-day life in a family where she and three of her children had varying degrees of OCD.

In a family in which several members show symptoms of OCD, the disorder often goes unnoticed until the child with the most severe symptoms is diagnosed, shedding light on undiagnosed issues affecting others.

Parent's Age of Onset as a Factor

Studies demonstrate that if a parent developed OCD at a young age, there is a greater likelihood that her OCD-affected child will also develop the disorder in early childhood, whether boy or girl. This, in tandem with other quickly accumulating data, overwhelmingly supports the conclusion that OCD is a highly heritable, genetically based disorder in the same way that a vulnerability to other diseases — for example, certain types of cancers, heart disease, and Alzheimer's disease — is handed down from one generation to the next. It ties a child's vulnerability to OCD to the nature component of the nature-versus-nurture debate on how a disease may be transmitted between a parent and a child.

The fact that OCD is in large part genetically determined means that if you have OCD and your child has developed the disorder you did not “give” it to him by modeling certain types of behavior in your home. Even if scientists cannot yet say with any certainty which genetic mutation “causes” the intergenerational transmission of OCD, after decades of family and twin studies now augmented by genetic research, they can say without question that genes trump environmental influences in the transmission of OCD.

It has also been noted that in cases where both a parent and child have OCD, the expressions or symptoms of the disorder appear to differ widely for each. And so for reasons not understood, it is rare for a parent with OCD to have the same symptoms as her child. For example, a mother with a fear of contamination would be more likely to have a child whose OCD manifests as an ordering compulsion as opposed to a contamination fear.

If You Discover Your Own OCD

Because OCD and other another anxiety disorders (such as panic disorder or social anxiety disorder) run in families, you may find that more than one member of your family has OCD. If OCD is present in a parent or sibling, your child has a 20 percent greater chance of developing the disorder. However, given the fact that diagnosis and treatment were less common before the mid 1990s, a parent or older sibling's OCD may not have been previously recognized.

In this scenario, the first time you see symptoms of OCD in yourself or another family member may be when you recognize its presence in your child. Perhaps you've unknowingly had symptoms since childhood. This increasingly common phenomenon was the subject of a December 2007 story in Newsweek titled, “Your Child's Disorder May Be Yours, Too.”

It describes a mother in her fifties who identified her own attention deficit disorder after her two sons received treatment for ADHD. After learning about the disorder, she began to think about her own lifelong difficulty focusing on simple tasks such as paying bills on time and remembering appointments. When she got out her old elementary school report cards, she found descriptions of herself as “disorganized” and “has trouble paying attention.” She was both relieved and prepared when she then went to her son's psychologist and received a formal diagnosis of her own ADHD. Her subsequent treatment with a stimulant medication and cognitive therapy has helped this mother manage her problem, and in her view, made her a better “coach” in her sons' treatment.

As summed up in the Newsweek article: “Children made miserable by a psychiatric or developmental disorder may not always want company, but they often long for evidence that they aren't the only ones putting a burden on the family … Having a parent with the same quirks who can talk about it eases the guilt a child may feel. The child has a fellow traveler, and in some cases, maybe more.”

If you discover your own OCD at the same time the disorder is diagnosed in your child, you may be uncertain whether to seek a diagnosis or treatment right away. Perhaps you feel the best course of action is to concentrate on your child's problems, while deferring your own. However, as noted above, the opposite may be true. It can be helpful for a child to observe a parent receive a formal diagnosis and treatment at the same time or prior to his own. The parent essentially serves as a model, demonstrating what's to come for the child.

Here's how one mother of a seven-year-old daughter describes the experience.

This mother is well equipped to help her daughter face the onset of OCD because her own OCD is being treated, and because she accepts OCD as a disorder that runs in her family. If you are a parent with OCD you must dispense as soon as possible with any guilt you may feel about being the “cause” of your child's disorder. All children are the sum of their genetic and environmental inheritances. The prerequisite to healing is self-acceptance. Eventually you may even be able to see a positive side of the OCD and be able to share this perspective with your child.