**4. Research course**

First degree relatives of patients are key elements in the study of endophenotypes. They are considered at-risk individuals. Even so, only a relatively small percentage of siblings of an individual with ASD will develop such disorders, but a larger proportion is expected to exhibit phenotypes that may fulfill the requirements of endophenotypes.

It has been shown that siblings of patients with ASD as well as other first degree relatives sometimes exhibit social, communication, and/or learning deficits, and ASD are more frequent in them than in the general population. Several possible endophentoypes for ASD have been proposed so far and are related with language and communication and/or with cognition, anatomy, or neurophysiology.
