Background: As part of our goal to involve more clinicians from Spanish speaking countries in psychiatric genetics, we have organized this educational session, to review the current findings in the field. In this first lecture, I will introduce the principles of genetic mapping for the following lectures, for a non-specialist audience.

Methods: I will review the principles of genetic mapping studies in psychiatric disorders, comparing Mendelian and complex inheritance, for a non-geneticist Spanish speaking audience, using our results from Costa Rica, in our collaborations and in other recent studies on schizophrenia and bipolar disorder.

Results: Different strategies such as linkage and association, in families and population samples, will be discussed and compared, as well as the advantages of population isolates, using the example of our studies in Costa Rica. Genetic polymorphisms, high density genotyping, and sequencing will also be explained. We will briefly review how to follow up genetic variants found to be linked or associated to illness. The additional complexities in mapping and identifying genes for psychiatric genetics will be addressed, such as the definition of the phenotype under study and the identification and use of endophenotypes. The concept of heritability and missing heritability, its use and limitations will also be defined and explained.

Conclusions: A summary of the current findings on the genetic underpinnings for major psychiatric disorders including schizophrenia and bipolar disorder will be presented, as well as new lines of research on GxE interactions.