Clozapine: weight gain in a pair of monozygotic twins concordant for schizophrenia and mild mental retardation

Clozapine is an atypical antipsychotic known to cause considerable weight gain. The extent to which genetic factors determine weight gain is unknown. Here we report on a pair of female monozygotic twins concordant for schizophrenia and mild mental retardation who were treated with clozapine over 5.5 years. One twin gained a total of 53.1 kg and had a weight of 107.5 kg (BMI=38.1 kg/m2) at the end of the observation period. The other twin gained a total of 48.2 kg and finally had a weight of 100.4 kg (BMI=33.8 kg/m2). Because both patients experienced considerable weight gain during treatment, our observation suggests that the antipsychotic-induced weight gain is under strong genetic control.