by Joye C. Anestis
I almost never watch reality programs about mental illness. Without fail, they frustrate me because they are generally full of misinformation. Therefore, I have never watched the A&E program Hoarders...if any of you have and want to offer up some insight into it, please contribute to the comments below. Even though Mike and I don't watch Hoarders (which is remarkable considering the number of hours we spend in front of the TV each week), it does seem to be pretty popular and represents a recent public fascination with compulsive hoarding. Take, for example, the documentary, musical, and television movie versions that have emerged of Grey Gardens, the story of "Big" and "Little" Edie Beale. So I thought today it'd be interesting to look into the literature on compulsive hoarding...specifically, how common is compulsive hoarding and are hoarding behaviors the result of genetic or environmental factors (or both)?
A recent twin study published in the American Journal of Psychiatry by Allesandra Iervolino and colleagues attempted to answer this question. These authors utilized a large (almost 10,000 twins) registry of monozygotic (identical) and dizygotic (fraternal) twins in the UK. This is a general registry of twins and is not disorder specific (a very common approach to twin studies). Of the total group, 5,022 twins completed the Hoarding Rating Scale - Self-Report. This group consisted of 2,053 twin pairs and 916 singleton twins.
Iervolino et al. found an overall prevalence rate of 2.3% in this sample. These individuals experienced hoarding symptoms to the degree that they were distressing and impairing. This rate is smaller than prevalence estimates reported in other studies, but the authors argue that measurement differences caused this disparity. Specifically, earlier studies used a unidimensional measure of hoarding, whereas the present study utilized a more comprehensive measure of hoarding. The use of a narrow construct definition in earlier studies may have resulted in an overestimation of prevalence. Interestingly, a significantly higher rate of severe hoarding was observed in males compared to females. This is consistent with the results in other epidemiological studies, but is in sharp contrast to hoarding samples derived from clinical populations. These samples are predominantly female, perhaps indicating the female hoarders are more willing to seek help.
While these fascinating sex differences emerged, analyses investigating the heritability of hoarding could only be conducted on the female twins...only a small number of male twins participated in the survey, so the subject number of the heritability analyses was 4,355 female twins. As might be expected from anecdotal examples of familial hoarding (such as the Beales), there appears to be a significant genetic contribution to hoarding behavior. About 50% of the variance in compulsive hoarding is accounted for by genetic factors, with non-shared environmental factors and measurement error accounting for the other 50%. Let me briefly explain how twin studies work to help make these results make sense. Monozygotic (identical) twins share 100% of their genetic material, whereas dizygotic (fraternal) twins share about 50%. So if genes are important, we expect identical twins to be more similar than fraternal twins. But environmental factors complicate things. Shared environmental factors influence the extent to which genetic factors do not account for twin similarity (usually, twins grow up in the same environment, so we must tease apart genetic influence from the influence of having the same experiences). Nonshared environmental factors are those that genetic and shared environmental influence cannot account for (the most direct estimate of these are the degree to which identical twins differ). So these are the things that make family members more different than alike. So in this study, genetics and then nonshared environmental influence explained most of the variance in hoarding in women. Environmental factors shared by siblings did not contribute to the liability for hoarding. These findings are consistent with previous research on obsessive-compulsive disorder (of which hoarding is considered to be a subtype) and other anxiety disorders. There is a large genetic component to anxiety but unique environmental influences dictate how that anxiety manifests.
Certainly, this study has its limitations - such as reliance upon a self-report survey and the low number of men - but it represents an important contribution to understanding this phenomenon. At present, research is underway to identify specific genes that contribute to this and many other disorders. Hoarding is often devastating to individuals and families, and people who hoard often respond poorly to antidepressants and behavior therapy. Research like this that helps us understand where hoarding comes from will ultimately aid us in figuring out how to treat it.
If you would like to learn more about anxiety disorders and their treatment, we recommend searching our online store of scientifically-based psychological resources.
Joye Anestis is a doctoral candidate in clinical psychology at Florida State University.
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