Is compulsive hoarding a genetically and neurobiologically discrete syndrome? Implications for diagnostic classification.

Although standard diagnostic classifications consider obsessive-compulsive disorder (OCD) to be a single diagnostic entity, it has become clear that it is a heterogeneous disorder, with great variability in clinical presentation. This heterogeneity has complicated the interpretation of clinical, neurobiological, and genetic studies in OCD. Therefore, researchers have sought to identify clinically meaningful phenotypes that might be more homogeneous and heritable to facilitate our understanding of the etiology and pathophysiology of OCD and ultimately lead to improved treatments (1). Factor analytic studies have consistently identified four principal OCD symptom dimensions: 1) harm-related, aggressive, sexual, and religious obsessions with checking compulsions; 2) symmetry obsessions with arranging and repeating compulsions; 3) contamination obsessions with cleaning compulsions; and 4) hoarding and saving symptoms (1, 2). These symptom factors are relatively stable over time and show different patterns of genetic inheritance, age at onset, comorbidity, and treatment response (see 1 for review). Cluster analyses, which seek to identify mutually exclusive, categorical subgroups, indicate that some of these symptom factors, such as hoarding, may constitute discrete subtypes of OCD (3, 4). Hoarding is defined as the acquisition of and inability to discard items, even though they appear (to others) to have no value (5). Hoarding behavior has been observed in several neuropsychiatric disorders, including schizophrenia, dementia, eating disorders, autism, and mental retardation, as well as in non-clinical populations, but it is most commonly found in OCD (6). 30% to 40% of OCD patients report hoarding and saving symptoms (6–8), and about 10% to 15% have hoarding as their most prominent symptom factor (3, 6). Compulsive hoarding is most commonly driven by obsessional fears of losing important items that the patient believes will be needed later, distorted beliefs about the importance of possessions, excessive acquisition, and exaggerated emotional attachments to possessions (5). Compulsive hoarding and saving leads to clutter that can cover living and work spaces, rendering them unusable. Hoarding frequently causes significant impairment in social and occupational functioning. In severe cases, it can produce health risks from infestations, falls, fires, and inability to cook or eat in the home (6). In this issue of the Journal, Jack Samuels, Ph.D., et al. report results from the OCD Collaborative Genetics Study, finding “suggestive” linkage of compulsive hoarding to a marker on chromosome 14 in families with OCD. The linkage became stronger when only families with two or more family members with compulsive hoarding were tested. Compulsive hoarding is well known to run in families. Hoarding behaviors are significantly more prevalent in the relatives of hoarding OCD patients than nonhoarding OCD patients (9). In the OCD Collaborative Genetics Study, hoarding was the most strongly familial of the OCD symptom factors, with robust correlations among sibling pairs (10). Only two previous genetic studies have examined the hoarding phenotype. Lochner et al. (8) found that the met/met (L/L) genotype of the catechol O-methyltransferase val158met polymorphism on chromosome 22q11 was significantly more prevalent in Afrikaner OCD patients with