2

Psychiatric disorders are complex hereditary (non-Mendelian) diseases involving genetic and environmental factors (climate, stress, diet, infections, etc.). The identification of these genetic factors begins with the observation of an excess of familial cases (familial aggregation), and then continues with the demonstration that this excess of familial cases is due to genetic factors (genetic component), finally going on to analyze this genetic component by searching for genetic variants associated with psychiatric disorders (or clinical aspect). The discovery of epigenetic mechanisms has added an additional nuance to the supposed “fatalism” linked to the “genetic code,” whose expression is modulated by a set of environmental factors. In the near future, the fields of application of psychiatric genetics should help us achieve earlier and more accurate diagnoses, as well as aiding the development of targeted and personalized treatments.