Back in 1915, a young Kentucky boy had blasphemous thoughts that he feared would land him in hell. During the 1940s his young daughter experienced the same thing. Did she inherit the tendency toward such distressing, repetitive thoughts from him?

Very possibly, if the results of a study conducted by Gerald Nestadt, M.D., a psychiatrist with the Johns Hopkins Medical Institutions in Baltimore, and colleagues are correct. They suggest that obsessive-compulsive disorder (OCD) very much runs in families. Their study appears in the April 6 Archives of General Psychiatry.

"I think it is an excellent study," Donald W. Black, M.D., a psychiatrist and an OCD researcher at the University of Iowa College of Medicine in Iowa City, told Psychiatric News. "It is well-designed, it’s very carefully done, the sample size is sufficient, and this study, along with the family study that Dr. David Pauls published a number of years ago, establishes, in my opinion, that obsessive-compulsive disorder is familial beyond question."

The role of heredity in OCD has long been suspected. In fact, several twin studies have buttressed this suspicion. However, the numerous family studies that explore the possibility have either been flawed or have produced conflicting results. For instance, while the investigation by Pauls implied that the condition is inherited, but a study conducted by Black did not. So Nestadt and his team decided to conduct a familial study that would provide a rigorous test of whether OCD is inherited. Such a study was especially urgent, they contended, since the World Health Organization has named OCD one of the 10 most disabling medical conditions worldwide.

They selected as their subjects 80 persons who had been diagnosed with OCD at five different specialty clinics in the Washington-Baltimore area. (By using subjects from various clinics instead of from only one, they hoped to avoid selection bias.) The mean age at which these individuals had started experiencing OCD symptoms was 11 years; 75 percent had commenced by age 14. Seventy-three controls were then selected by a random-digit dialing procedure conducted by a Baltimore survey research contractor. Interviews were then conducted on 343 first-degree relatives of the subjects and on 300 first-degree relatives of the controls to see whether they were experiencing obsessions, compulsions, or both..

The interviewers—psychiatrists and clinical psychologists—did not know whether the persons they interviewed were related to subjects or controls. Audiotaped interviews as well as comprehensive diagnostic evaluations by the interviewers of all the relatives interviewed were then turned over to two psychiatrists who decided, on the basis of DSM-IV criteria, which had OCD. The prevalence of OCD among relatives of subjects was then compared with the prevalence of OCD among relatives of controls.

OCD was much more widespread among relatives of persons with OCD than among relatives of persons without it, the study investigators found—11.7 percent versus 2.7 percent, a highly significant difference. In fact, the odds of having OCD were nearly five times as great among relatives of subjects than among relatives of controls. Both results suggest that OCD is inherited.

Also of interest, the researchers discovered, was that while subject relatives had an excess of both obsessions and compulsions compared with those of control relatives, they especially had an abundance of obsessions, implying that the tendency to obsess is particularly inheritable.

Results of a study such as this, of course, do not prove that OCD is inherited. "The finding that OCD is familial is a necessary, albeit not sufficient, condition for genetic etiology," concludes the researchers. In other words, the proof will come only when a gene or genes responsible for OCD are identified.

Unfortunately, that hasn’t happened yet, Nestadt said in an interview. In fact, he added, no specific chromosomal regions have yet been identified as possible geographic sites for OCD genes. Such discoveries may well come, though, now that psychiatric genetics research is getting hot.

Also complicating a slam-dunk case for the inheritability of OCD is another finding from the study by Nestadt and his team. Whereas 13.8 percent of relatives of subjects who had developed OCD at an early age got OCD as well, none of the relatives of late-onset OCD had. So there may be an inherited form of OCD, acquired while young, and a noninherited type, developed later in life.