The 1950s marked the beginning of our modern conceptualization of pharmacogenetics as a distinct discipline. In 1959, the German human geneticist Friedrich Vogel first introduced the term “pharmacogenetics.”5 Since then, many researchers have used genetic techniques to examine variability in drug response across patients and populations. One of the first known studies in psychiatry identifying a potential inherited basis of drug response summarized an investigation of 41 first-degree relative pairs treated with tricyclic antidepressants (TCAs).6 Thirty-eight of the 41 relative pairs were concordant for response. In the 1960s and early 1970s, Pare et al. demonstrated that subgroups of relatives followed in assessments of antidepressant treatment response exhibited striking similarities in their outcomes to treatment.7, 8 In these rare instances where family members were assessed, all 12 first-degree relative pairs receiving monoamine oxidase inhibitors (MAOIs) and 10 of 12 first-degree relatives receiving TCAs were concordant for response. Around the same period, Alexanderson et al. investigated steady-state plasma concentrations of nortriptyline in twins and postulated that the variability observed in the data could be due to genetic differences in ability to metabolize
