Lack of association of apolipoprotein E polymorphism in obsessive-compulsive disorder

Link Between Obsessive-Compulsive Disorder and ApoE Gene Polymorphisms

Objective

Many researchers have considered obsessive compulsive disorder (OCD) to be a neurodegenerative disease just like Alzheimer's disease (AD). The most studied gene in neurodegenerative diseases is apolipoprotein E (ApoE) gene, and ApoE ɛ4 allele in particular. Although a small number of studies have explored the relationship between ApoE gene polymorphisms and OCD, the link between age at onset of OCD, its subtypes and ApoE gene polymorphisms has not been revealed so far. For this purpose, in our study, the relationship of ApoE gene polymorphisms with age at onset of OCD and its subtypes has been investigated to reveal their neurodegenerative connections.

Patients and Methods

ApoE gene polymorphisms of 64 OCD and 28 healthy cases were studied using a LightCycler480 real-time PCR platform.

Results

A statistically significant difference was found between groups of patients with early- and late-onset OCD in terms of age (p = 0.03), educational level (p = 0.00) and marital status (p = 0.002). ApoE ɛ4ɛ4 genotype, the prevalence of which is below 2% in healthy individuals, was not detected in our control groups; however, it was identified in 5.1% of our OCD cases. Correlation analysis revealed the presence of a potentially significant link between the hoarding obsession and presence of the ɛ4ɛ4 genotype. A significant correlation was detected between the presence of the ɛ3ɛ3 allele, the symmetry obsession and associated ordering compulsion in patients with OCD (p<0.005).

Conclusion

The ApoE gene polymorphism profile and age of onset in OCD patients may play critical roles in the development process of neurodegenerative characteristics of the disease. The small number of cases and the inability to perform brain imaging in patients to detect the neurodegenerative link in OCD are limitations of our study. In this respect, we suggest conduction of further studies with a greater number of patients who will also undergo brain imaging studies. In addition, OCD patients have other genes associated with neurodegenerative diseases that can be screened.

Overview of genetics and obsessive-compulsive disorder

This paper reviews the current state of research into the genetics of obsessive-compulsive disorder (OCD). Heredity has a major role in OCD etiology. This evidence comes from several methodological approaches such as family, twin, and segregation analysis studies. A major single gene effect as well as a polygenic hypothesis has been suggested based on segregation studies. In addition, candidate gene association and linkage analyses have shown not only one gene, but a few interesting genes and areas of the genome that may be relevant in OCD. In this search for genes, new definitions of the OCD phenotype have emerged, and some of them may be considered intermediate phenotypes between the gene effect and OCD-DSM-IV diagnosis. The phenotypic and genetic heterogeneity of OCD magnifies the challenge of locating susceptibility genes; at the same time, the identification of vulnerability genes will elucidate the identification of subtypes or dimensions of the disorder. Therefore research strategies that take advantage of clinical subtyping and that redefine the OCD phenotype in the context of genetic studies may potentially contribute to the nosology of OCD and ultimately pathophysiology. There is a lack of understanding about how genes and environment interact in OCD. However, there are some reports that will be discussed, which have attempted to evaluate how the environment contributes to OCD.

Obsessive-compulsive alcohol craving is not associated with Apolipoprotein E genotype

This study examined a possible association with obsessive and compulsive alcohol craving in 192 alcohol-dependent patients undergoing detoxification treatment. Statistical analysis revealed no significant association between Apolipoprotein E polymorphism and obsessive-compulsive alcohol craving (analysis of variance: F=1.11, P=0.358).