ABSTRACT
Some of the most important work on neurobehavioral genetics is in the study of psychiatric disorders in twins. As you will recall, monozygotic twins share identical genotypes and dizygotic twins share, on average, 50% of genes (alleles) in common. While we know that there is a genetic component to schizophrenia, most estimated concordance rates among monozygotic twins range from 40 to 50%, and for dizygotic twins, most estimates are below 20%.1 This tells us that genes are involved in schizophrenia, but the environment also plays a major role. So, those carrying one or more allelic configurations are susceptible to environmental events that produce the disease. Just what the genetic configurations and environmental events are constitutes a subject of intensive study. Environment can be broadly construed and
can include internal as well as external events. Thus, exposure to drugs, hormones, toxins, or teratogens in utero, nutritional status, viral infections, early rearing conditions, and social situations in adulthood may all be considered as “environment.”
