Eating disorders
Studies on the pathology of Eating disorders
Eating disorders are mainly manifested by symptoms such as abnormal eating behaviors and distorted body images (leading to a drive for thinness, intense fear of gaining weight, and body dissatisfaction), and include anorexia and bulimia nervosa, which affects mostly young women. Particularly in the case of anorexia nervosa, clarifying its mechanisms is an important issue, as mortality rates are high despite the predilection for young age groups, and it is difficult to treat.
Some researchers regard eating disorders as multifactorial; they develop due to multiple factors from the congenital physical constitution to environments after birth. Among these factors related to eating disorders, the congenital physical constitution (vulnerability to eating disorders and tendency of their course) has been suggested to be associated with genes. Genetic factors have been reported to be responsible for approximately 60% of the influences on vulnerability to eating disorders. Although the mechanisms of the diseases cannot be fully elucidated only by genes, identifying genes associated with eating disorders and their activities in the body is likely to contribute to the clarification of such mechanisms and development of new treatment methods.
1. Genetic factors
In Japan, a multicenter collaborative study is currently being conducted by the Japanese Genetic Research Group for Eating Disorders, led by the National Center of Neurology and Psychiatry (Department of Psychosomatic Research, National Institute of Mental Health), and the University of Occupational and Environmental Health (Division of Psychosomatic Medicine, Department of Neurology) is also participating in it, with cooperation from a large number of patients.
This study has revealed the influences of the genetic polymorphism of ghrelin as a feeding-promoting peptide on the rate of weight gain in anorexia nervosa, as well as an association between the disease and genetic polymorphism of the fatty acid amide hydrolase as an endocannabinoid catabolic enzyme, reportedly involved in multiple physiological functions, including appetite control.
2. Environmental factors
As another characteristic of eating disorders, a close association with environments after birth has also been suggested. For example, in Japan, the incidence of eating disorders has been rapidly increasing since the late 1990’s, and this cannot be fully explained only by the genetic background.
Statistics confirm that the incidence is higher in countries more markedly influenced by Western culture, suggesting that the cultural view that thin bodies are beautiful and comparisons between one’s own body shape and those of models highly publicized through the media may be associated with the pathology of eating disorders. Under these circumstances, we are currently examining the applicability of a new treatment method, in which visual stimuli related to such comparisons of the body shape are produced, and patients’ brain activity when they compare their own body shapes with others is visualized using fMRI (functional magnetic resonance imaging).