User Tools (skip):
Some bulimics have a harder time breaking out of the binge and purge cycle than others. Some recover using short-term treatment approaches while others become chronic cases.
Psychiatry professor Howard Steiger, director of the Eating Disorders Program at the Douglas Hospital, and fellow researchers at McGill have found that a substantial proportion of individuals with bulimia have a genetic predisposition to impulsivity.
They don't believe there is a "bulimia gene," but they are looking at genetic and environmental factors that may make certain individuals more susceptible to bulimia.
Mood, impulse control and eating behaviour are all regulated by a chemical messenger called serotonin. Studies in both people and animals have shown that reducing serotonin transmission in the brain produces compulsive, or binge, eating.
There are a number of different genes that control serotonin activity. For each of these genes, there is a range of different polymorphisms, or forms. These different forms control how much serotonin the brain produces and how quickly the nerves reuptake, or reabsorb, serotonin once it has been produced. They also control the sensitivity of the serotonin neuroreceptors — brain cells that are specialized to receive serotonin.
Steiger's research has shown that individuals differ with respect to a gene called the serotonin transporter gene. Those who have a certain form of the gene called the S-allele have lower serotonin reuptake. These individuals are more impulsive, have greater mood instability and have suffered more childhood abuse than other types of bulimics. They are also less responsive to treatment than individuals with the alternative form of the gene.
Steiger is investigating whether various environmental factors can interact with the S-allele to make vulnerability to bulimia worse. For example, his team has found that adult women with bulimia who had been severely abused as children had prominent reductions of serotonin activity many years later. As well, dieting can also lower serotonin activity. Even modest dieting has dramatic effects on the activity of the serotonin system.
"You may carry a gene," says Steiger. "Your development may turn the volume up on the gene and then dieting, later in life, flips the switch."
Steiger takes pains to say that these environmental factors do not cause bulimia, per se. He goes on to explain, however, that within the larger group of bulimics, there are two sub-groups. One group develops a relatively circumscribed form of bulimia. "They binge, they purge, they diet, but they don't show a lot of other disturbances," says Steiger. "Then there is another kind of pattern where you see people developing the bingeing, the purging, but they also have very, very dramatic mood problems. In this group they are much more impulsive, they have had much higher [rates] of childhood abuse, things like that."
Steiger and colleagues theorize that there are two routes to bulimia. Some people become bulimic due to dieting too much. The dieting deregulates their appetite and they start to binge. These people can be helped by getting them to stop dieting. Other people become bulimic due to more pervasive problems, such as a genetic predisposition to lowered serotinergic functioning, which then interacts with adverse childhood experiences.
"The new stuff off the press," says Steiger, "is we are also looking at the extent to which these [genetic] variations could predict the response to treatment." Treatment for bulimia is generally focused on getting people to interrupt their binge eating and develop a better sense of self. According to Steiger, 50 to 60 percent of bulimics overcome the disorder after a reasonable time period. About 20 percent of bulimics go on to become chronic. Individuals in the chronic group have a tendency to be more impulsive, and there are some indications that child abuse is also more present. Steiger's research is showing that perhaps the less responsive group is more compromised in terms of serotonin function.
Knowing about these two types of bulimia may help clinicians individualize treatment. Currently, all types of bulimia are treated with a multidimensional treatment, comprising medication such as selective serotonin reuptake inhibitors, nutritional intervention and psychological therapy. According to Steiger, dietary changes alone appear to be an effective treatment for bulimics without the impulsivity trait. Thus, clinicians could save the costly, multidisciplinary interventions for the less-responsive cases in which impulsivity plays a role.