Background The role of the promoter polymorphism (5HTTLPR) of the serotonin transporter gene (SLC6A4) in psychiatric illnesses has been studied extensively. Serotonergic function also regulates many central nervous system, including appetite and feeding behaviors. The 5HTTLPR short allele was found to be associated with increased body mass index and obesity risk among the general population. No data is available to support generalizability of such association among psychiatric population. Methods We examined the relationship between BMI and the 5HTTLPR genotype in a large sample of 1831 psychiatric patients at Mayo Clinic, Rochester, Minnesota, using a retrospective chart review. Results Average BMI among groups with the short/short (28.29±7.27 kg/m 2 ), the short/long (28.07±6.45 kg/m 2 ) and the long/long (28.15±7.51 kg/m 2 ) genotypes of 5HTTLPR were not statistically different. This negative association persisted even with the sub-analysis of the Caucasians. However, we observed an increased rate of obesity among our psychiatric patient sample compared to the general population of Minnesota (36.6% versus 27.6%, p =0.0001 for males, 30.3% versus 24.4%, p =0.0001 for females). Also, sub-analysis showed female inpatients to have a significantly higher average BMI than outpatients (28.64±8.08 kg/m 2 versus 27.13±6.92 kg/m 2 , p =0.026). This confirmed a significant association between mental health disorder and BMI. Limitations Retrospective study design with limited control for potential confounders. Conclusions In this large sample of psychiatric patients we found no significant association between 5HTTLPR genotype and BMI, which is different from the case with general population reported in the literature.
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