Etiology of Hoarding Disorder in Monozygotic and Dizygotic Twins: An Integrated Genetic, Environmental, and Behavioral Model

 The “Obsessive-Compulsive and Related Disorders” chapter in DSM-5 involves a series of conditions supposed to be etiologically related to obsessive-compulsive disorder (OCD). The present study aimed to determine the heritability rate and the role of environmental factors of OCD in monozygotic and dizygotic twins.

The research was conducted based on a twin study design. A total of 672 twins (MZ=474; DZ=202) were selected from twins associations in megacities in Iran in 2019. The required data was collected using the Hoarding Rating Scale and the Self-Report of Zygosity. Twin modeling methods were employed to decompose the variance in the liability to hoarding disorder (HD) into additive genetic and shared and non-shared environmental factors. The data were analyzed by SPSS, STATA, and M-plus.

The results showed that the correlation rate of the identical group was equal to 0.58, while it was 0.26 in the non-identical group. The best-fitting model for HD was the AE model. Additive genetic factors explained more than 50% of the phenotype variance of HD and the other phenotype variance of this disorder can be explained by non-shared environment.

The comorbidity pattern of the additive genetic factor and non-shared environment plays an important role in HD phenotype. On the other hand, the role of common environment, such as siblings and parenting style, was very small in the etiology of HD.