Found: A Genetic Basis for SAD and Bulimia Nervosa

Seasonal affective disorder (SAD) and bulimia nervosa are both characterized by overeating and a depressed mood. Initial data from the University of Toronto point to a possible role for genes mediating the enzyme tryptophan hydoxylase (TPH), essential for serotonin synthesis in both disorders.

Dr. Robert D. Levitan and colleagues initially tracked 3 serotonin genes involved in regulating TPH, the serotonin 2C receptor (HTR2C), and the serotonin transporter 5-HT2 in women with either SAD and carbohydrate craving/increased eating or bulimia nervosa. They also collected parental control triads and cases with matched controls; all were genotyped for TPH, HTR2C, and 5-HT2 polymorphisms. In an earlier study, the researchers found evidence of dysfunction at or downstream from central serotonergic receptors in female patients with SAD, giving further evidence of a serotonergic dysfunction in patients with SAD (Arch Gen Psychiatry 55:244, 1998).

In the current study, recently presented at the American Psychiatric Association meeting in Washington, Dr. Levitan reported an association between SAD and the TPH L-allele in both the parental control sample (22 triads) and the extended sample (n=47). In bulimia nervosa, the extended sample showed a significant finding in the same direction as for TPH (n=39), but the parental control sample did not reach statistical significance. No significant findings were reported for either HTR2C or 5-HTT. It is also important to remember that not all bulimic patients are depressed.