Genetics Most Important Factor in Compulsive Hoarding

Pauline Anderson

August 27, 2009

August 27, 2009 — Genetic factors contribute to at least half of all compulsive hoarding, a new study suggests.

In the first twin study to examine hoarding, investigators at the Institute of Psychiatry in London in the United Kingdom found that genetics accounted for approximately 50% of the variance in compulsive hoarding and that rates among male twins (4.1%) were double those in female twins.

Severe hoarding is not just collecting stamps or coins, it is the accumulation of so many mostly worthless possessions, and being unable to discard them, that carrying out normal activities at home is difficult.

According to the study, compulsive hoarding is associated with substantial psychiatric comorbidity including mood disorders, social phobia, and personality disorders, in addition to obsessive-compulsive disorder. Therapeutic response to antidepressants and behavior therapy is poor or partial at best.

Although previous research has shown that hoarding runs in families, researchers were uncertain of the extent of its heritability, said study investigator David Mataix-Cols, PhD. "This is the first study that actually tells us that a big proportion of this condition is due to genes. But it's clearly not only genes — you need some environmental factors as well," he told Medscape Psychiatry.

The study was published online August 17 in the American Journal of Psychiatry.

The study included monozygotic and dizygotic twins from the TwinsUK adult twin registry. Started in 1993, the registry consists of Caucasian twins aged 16 years and older from all over the United Kingdom.

Researchers sent the Hoarding Rating Scale–Self Report (HRS-SR) questionnaire to all 8313 active twins in the registry. The HRS-SR is a brief, self- administered instrument that rates clutter, difficulty discarding, excessive acquisition, and distress and impairment caused by hoarding, with a score ranging from 0 to 40.

For this analysis, researchers used a cut-off of 17, which has previously been used in research studies of compulsive hoarders, to determine the presence of severe symptoms of hoarding.

Of the questionnaires sent out, 5022 were returned. These were from 2053 sets of twins (1096 monozygotic and 957 dizygotic) as well as 916 singleton twins (456 monozygotic and 460 dizygotic). Close to 90% of the sample were women.

The study found that the overall prevalence of severe hoarding was 2.3%, and the mean HRS-SR score was about 21.

More Prevalent in Men

The hoarding prevalence was significantly higher among men (4.1%) than women (2.1%). This contrasts with the higher number of women seen in clinical practice, perhaps because many more women seek treatment, said Dr. Mataix-Cols.

To determine genetic and environmental influences on hoarding, the researchers used a subsample of 4355 women. They determined that genetic factors accounted for at least 50% of the variance in compulsive hoarding.

In addition, Dr. Mataix-Cols said, nonshared environmental factors that include such things as abuse, along with measurement error, accounted for much of the rest of the variance in compulsive hoarding.

"We know from the literature that sexual assault or a history of abuse and traumatic experiences in general are common in compulsive hoarding," said Dr. Mataix-Cols. It is possible that traumatic experiences interact with genes to trigger compulsive hoarding, he added.

In contrast, the study showed that shared environmental factors — parental practices, for example — did not contribute to individual differences in the likelihood of compulsive hoarding.

According to Dr. Mataix-Cols, scientists are beginning to search for candidate genes for compulsive hoarding in the context of Tourette's syndrome and obsessive-compulsive disorder, but results so far have been inconsistent.

He added that the results of this current study will likely motivate the search for candidate genes in compulsive hoarders who do not have other psychiatric disorders.

Loss and Abandonment

Some research has suggested that compulsive hoarders are trying to fill a gap in their lives. Loss and abandonment are certainly recurring themes for many patients with hoarding problems, said Dr. Mataix-Cols. "There are lots of reports of loss in these people: they talk about the death of relatives, they talk about losing their homes."

Compulsive hoarding is often considered a symptom of obsessive-compulsive disorder, although in the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, it is only mentioned as a symptom of compulsive personality disorder. There is a push in some circles to have it included as a separate condition in the next version of the manual.

"What has become quite clear now is that a large proportion of severe hoarders, probably more than half, do not meet strict criteria for obsessive-compulsive disorder," said Dr. Dr. Mataix-Cols.

House of Clutter

Typically, patients with a compulsive hoarding problem have covered virtually all surfaces of their home with clutter. They sometimes cannot sleep in their bed, take a shower, or cook because of clutter and are often too ashamed to invite people into their homes. "One patient described it to me as C.H.A.O.S., which is an acronym for Can't Have Anyone Over Syndrome," said Dr. Mataix-Cols.

Extreme cases can result in injury or even death. Patients have been known to be crushed when large possessions fall on them or to get burned when a fire breaks out amidst paper clutter. Newspapers, magazines, books, letters, and lists are some of the most commonly hoarded items, along with old clothing.

Asked by Medscape Psychiatry to comment on the study, Joe Bienvenu, MD, associate professor of psychiatry, Johns Hopkins University, Baltimore, Maryland, described it as "exciting."

"It tells us something that our group and other groups have suspected based on family studies — that what's running in these families is not mediated by having a shared environment, and so it argues for some kind of genetic mechanism."

However, he said the study did not convince him that compulsive hoarding is a condition separate from obsessive-compulsive disorder. When talking about people who feel an illogical urge to hoard, "it's hard for me to imagine what the form of this thing is, if not obsessive compulsive in nature," he said.

He is also not convinced that more men suffer compulsive hoarding. He pointed out that perhaps proportionately, "the men who filled out the questionnaire had a higher prevalence [of hoarding] than the men in the population."

The authors have disclosed no relevant financial relationships.

Am J Psychiatry. Published online August 17, 2009.

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